Created attachment 22514 [details]
Stack trace

Issue #59670 probably related.

I opened all files in  
apisupport/project/src/org/netbeans/modules/apisupport/project/ui/ 
without an exception being reported. 

I run a dev build on a fresh userdir, JDK 1.5.0. When it comes up, I use Ctrl-O
to open NbPlatformCustomizerModules.java. I click on the label "Platform
Modules" and an error is thrown.

Created attachment 22515 [details]
Log file

I was also able to reproduce the exception - just go to Tools > Options
and select Form Editor Settings node.

I have not clicked on the component. That was the problem. 
 
"#59677: core/windows suplies tabs to openide/explorer in a not public 
contract" 
 
new revision: 1.9; previous revision: 1.8 
done 
Checking in ide/golden/impl-deps.txt; 
/cvs/ide/golden/impl-deps.txt,v  <--  impl-deps.txt 
new revision: 1.18; previous revision: 1.17 

I just did a clean build with the updated sources and the NCDFE is still
there - go to Tools > Options and select Form Editor Settings node.
Reopening.

cvs -q ci -m "Missing / in name of package" 
Checking in src/org/netbeans/core/startup/NbInstaller.java; 
/cvs/core/startup/src/org/netbeans/core/startup/NbInstaller.java,v  <--  
NbInstaller.java 
new revision: 1.3 

Created attachment 22539 [details]
Double package definition

I guess this one is fixed, the diff belongs to ISE from ClassLoader. 

Verified.