Steps to reproduce:
- create Quote sample
- set BP in line 124
- start debugging
- enter any customer name, e.g. "xxx", debugger stops at BP
- open Variables and expand "customerName" variable
- press ellipsis button next to *_M_p value, Value window appears
- press Cancel in Value window
Result: Debugger error window appears with the message "mi_cmd_var_assign: Usage: NAME EXPRESSION."

GDB log is:

~"GNU gdb 6.8-debian\n"
~"Copyright (C) 2008 Free Software Foundation, Inc.\n"
~"License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>\n"
~"This is free software: you are free to change and redistribute it.\n"
~"There is NO WARRANTY, to the extent permitted by law.  Type \"show copying\"\n"
~"and \"show warranty\" for details.\n"
~"This GDB was configured as \"i486-linux-gnu\".\n"
&"/home/ap153252/.gdbinit: No such file or directory.\n"
(gdb) 
2-gdb-set print repeat 0
3-gdb-set backtrace limit 1024
4-file-exec-and-symbols  "/home/ap153252/NetBeansProjects/Quote_22/dist/Debug/GNU-Linux-x86/quote_22"
2^done
(gdb) 
3^done
(gdb) 
4^done
(gdb) 
5-file-list-exec-source-file
6cd /home/ap153252/NetBeansProjects/Quote_22
7-exec-arguments 
5^done,line="104",file="quote.cc",fullname="/home/ap153252/NetBeansProjects/Quote_22/quote.cc",macro-info="0"
(gdb) 
&"cd /home/ap153252/NetBeansProjects/Quote_22\n"
~"Working directory /home/ap153252/NetBeansProjects/Quote_22.\n"
6^done
(gdb) 
7^done
(gdb) 
8-break-insert -t main
9-exec-run
10info proc
8^done,bkpt={number="1",type="breakpoint",disp="del",enabled="y",addr="0x0804ac03",func="main",file="quote.cc",fullname="/home/ap153252/NetBeansProjects/Quote_22/quote.cc",line="113",times="0"}
(gdb) 
9^running
(gdb) 
9*stopped,thread-id="0",frame={addr="0x0804ac03",func="main",args=[],file="quote.cc",fullname="/home/ap153252/NetBeansProjects/Quote_22/quote.cc",line="113"}
(gdb) 
&"info proc\n"
~"process 629\n"
~"cmdline = '/home/ap153252/NetBeansProjects/Quote_22/dist/Debug/GNU-Linux-x86/quote_22'\n"
~"cwd = '/home/ap153252/NetBeansProjects/Quote_22'\n"
~"exe = '/home/ap153252/NetBeansProjects/Quote_22/dist/Debug/GNU-Linux-x86/quote_22'\n"
10^done
(gdb) 
11-stack-list-frames
11^done,stack=[frame={level="0",addr="0x0804ac03",func="main",file="quote.cc",fullname="/home/ap153252/NetBeansProjects/Quote_22/quote.cc",line="113"}]
(gdb) 
12-stack-list-arguments 1
12^done,stack-args=[frame={level="0",args=[]}]
(gdb) 
13-break-insert "/home/ap153252/NetBeansProjects/Quote_22/quote.cc:124"
13^done,bkpt={number="2",type="breakpoint",disp="keep",enabled="y",addr="0x0804ac7a",func="main",file="quote.cc",fullname="/home/ap153252/NetBeansProjects/Quote_22/quote.cc",line="124",times="0"}
(gdb) 
14-exec-continue
14^running
(gdb) 
14*stopped,reason="breakpoint-hit",bkptno="2",thread-id="0",frame={addr="0x0804ac7a",func="main",args=[],file="quote.cc",fullname="/home/ap153252/NetBeansProjects/Quote_22/quote.cc",line="124"}
(gdb) 
15-stack-list-frames
15^done,stack=[frame={level="0",addr="0x0804ac7a",func="main",file="quote.cc",fullname="/home/ap153252/NetBeansProjects/Quote_22/quote.cc",line="124"}]
(gdb) 
16-stack-list-arguments 1
16^done,stack-args=[frame={level="0",args=[]}]
(gdb) 
17-var-update * 
18-stack-list-locals --simple-values
17^done,changelist=[]
(gdb) 
18^done,locals=[{name="discount",type="int",value="-1"},{name="customerName",type="string"},{name="MySystem",type="System"},{name="response",type="char",value="-65 '\\277'"},{name="type",type="int",value="-1080727320"},{name="amount",type="int",value="134541300"},{name="MyCpu",type="class Cpu"}]
(gdb) 
19-var-create - * discount
20-var-create - * customerName
21-var-create - * MySystem
22-var-create - * response
23-var-create - * type
24-var-create - * amount
25-var-create - * MyCpu
19^done,name="var1",numchild="0",value="-1",type="int"
(gdb) 
26-var-show-attributes var1
20^done,name="var2",numchild="2",value="{...}",type="string"
(gdb) 
21^done,name="var3",numchild="1",value="{...}",type="System"
(gdb) 
22^done,name="var4",numchild="0",value="-65 '\\277'",type="char"
(gdb) 
23^done,name="var5",numchild="0",value="-1080727320",type="int"
(gdb) 
24^done,name="var6",numchild="0",value="134541300",type="int"
(gdb) 
25^done,name="var7",numchild="1",value="{...}",type="class Cpu"
(gdb) 
27-var-show-attributes var2
28-var-show-attributes var3
29-var-show-attributes var4
30-var-show-attributes var5
31-var-show-attributes var6
32-var-show-attributes var7
26^done,attr="editable"
(gdb) 
27^done,attr="noneditable"
(gdb) 
28^done,attr="noneditable"
(gdb) 
29^done,attr="editable"
(gdb) 
30^done,attr="editable"
(gdb) 
31^done,attr="editable"
(gdb) 
32^done,attr="noneditable"
(gdb) 
33-var-evaluate-expression var1
34-var-evaluate-expression var4
35-var-evaluate-expression var5
36-var-evaluate-expression var6
33^done,value="-1"
(gdb) 
34^done,value="-65 '\\277'"
(gdb) 
35^done,value="-1080727320"
(gdb) 
36^done,value="134541300"
(gdb) 
37-var-list-children --all-values var2
37^done,numchild="2",children=[child={name="var2.public",exp="public",numchild="1",value=""},child={name="var2.private",exp="private",numchild="1",value=""}]
(gdb) 
38-var-list-children --all-values var2.public
39-var-list-children --all-values var2.private
38^done,numchild="1",children=[child={name="var2.public.npos",exp="npos",numchild="0",value="4294967295",type="const size_t"}]
(gdb) 
39^done,numchild="1",children=[child={name="var2.private._M_dataplus",exp="_M_dataplus",numchild="2",value="{...}",type="std::basic_string<char, std::char_traits<char>, std::allocator<char> >::_Alloc_hider"}]
(gdb) 
40-var-list-children --all-values var2.private._M_dataplus
40^done,numchild="2",children=[child={name="var2.private._M_dataplus.std::allocator<char>",exp="std::allocator<char>",numchild="1",value="{...}",type="std::allocator<char>"},child={name="var2.private._M_dataplus.public",exp="public",numchild="1",value=""}]
(gdb) 
41-var-list-children --all-values var2.private._M_dataplus.public
41^done,numchild="1",children=[child={name="var2.private._M_dataplus.public._M_p",exp="_M_p",numchild="1",value="0x9e38104 \"xxx\"",type="char *"}]
(gdb) 
42-var-list-children --all-values var2.private._M_dataplus.public._M_p
42^done,numchild="1",children=[child={name="var2.private._M_dataplus.public._M_p.*_M_p",exp="*_M_p",numchild="0",value="120 'x'",type="char"}]
(gdb) 
43-var-assign  var2.private._M_dataplus.public._M_p.*_M_p 120 'x'
&"mi_cmd_var_assign: Usage: NAME EXPRESSION.\n"
43^error,msg="mi_cmd_var_assign: Usage: NAME EXPRESSION."
(gdb)