If the user's SS.INI contains a value for the
"Editor" property, then the DIFF command fails. 
(This property can be set in VSS in
Options...General...Editor for viewing files).  If
this property contains no value, then the DIFF
succeeds.

When the command fails, the stored version of the
file opens in the configured editor.  NetBeans
does not complete execution of the command until
the editor is closed.

Details of failed DIFF_USR_CMD:

Execution String:
cmd /X /C "(mkdir
\"C:\Projects\RFN20\Products\RiskConsole\current\SourceCode\servlets\search\\com\risklabs\servlets\search\.\"
2>nul || echo.) && cd /D
\"C:\Projects\RFN20\Products\RiskConsole\current\SourceCode\servlets\search\com\risklabs\servlets\search\"
&& \"C:\Program Files\Microsoft Visual
Studio\VSS\win32\SS.EXE\" cd -I- -Ybrians,ibfly21
\"$/RiskConsole/current/SourceCode/servlets/search\com\risklabs\servlets\search\"
&& \"C:\Program Files\Microsoft Visual
Studio\VSS\win32\SS.EXE\" workfold -I-
-Ybrians,ibfly21
\"C:\Projects\RFN20\Products\RiskConsole\current\SourceCode\servlets\search\com\risklabs\servlets\search\"
&& \"C:\Program Files\Microsoft Visual
Studio\VSS\win32\SS.EXE\" diff -DU  -I-
-Ybrians,ibfly21 \"AdvancedSearchParameters.java\" "

Standard Out:

Current project is
$/RiskConsole/current/SourceCode/servlets/search/com/risklabs/servlets/search
C:\Projects\RFN20\Products\RiskConsole\current\SourceCode\servlets\search\com\r
isklabs\servlets\search has been established as
the working folder for project
$/RiskConsole/current/SourceCode/servlets/search/com/risklabs/servlets/search.Diffing:
$/RiskConsole/current/SourceCode/servlets/search/com/risklabs/servlets/search/A
dvancedSearchParameters.java
Against:
C:\Projects\RFN20\Products\RiskConsole\current\SourceCode\servlets\search\com\r
isklabs\servlets\search\AdvancedSearchParameters.java

88,89c88,89
<         out.println("           conditionList["
+ ConditionField.CONDITION_L
<         out.println("           conditionList["
+ ConditionField.CONDITION_L
---
>         out.println("           conditionList["
+ ConditionField.CONDITION_L
>         out.println("           conditionList["
+ ConditionField.CONDITION_L
90a91,97
>         out.println("           conditionList["
+ ConditionField.CONDITION_N
>         out.println("           conditionList["
+ ConditionField.CONDITION_N
>         out.println("           conditionList["
+ ConditionField.CONDITION_N
>         out.println("           conditionList["
+ ConditionField.CONDITION_N
>         out.println("           conditionList["
+ ConditionField.CONDITION_N
>         out.println("           conditionList["
+ ConditionField.CONDITION_L
>         out.println("           conditionList["
+ ConditionField.CONDITION_L

Data Output:
[Against:]
[88,89c88,89,,89,,89]
[90a91,97,,97]

My platform is NB 3.4, VSS 6.0 (Build 8163)
running on Win2K SP2.