Created attachment 968 [details]
The exception thrown.

Following exceptions occurred only on Windows.

Sorry my comment is not valid.

*** Issue 10990 has been marked as a duplicate of this issue. ***

this prevents the form editor from opening .form files, definitely a showstopper 

Make sure that you use proper version on XML parser. In the other words we
require JAXP 1.1 and compliant parser at classpath.

Could you check it?

I am attaching ide.log (for sureness), but I am running absolutely the same
build on JDK1.3 (the only change in my environment is changing JDK from 1.3 to
1.2.2 and back) and run on JDK1.3 is without problems. The first jaxp on
classpath (I hope) is lib/ext/jaxp.jar.

Created attachment 979 [details]
IDE log from first start on JDK1.2.2

I expect that you have an old version of jaxp.jar. Check {$jre}/lib/ext and
{$netbeans}/lib/ext. 
You MUST avoid jaxp.jar that in its manifest declares
JAXP version 1.0 and is marked as sealed. The sealed flag protect "upgrading"
java package content by package content defined in different jar.

As simple test use
Class.forName("org.xml.sax.EntityResolver").getProtectionDomain().getCodeBase().getLocation().toExternalForm();
inspect resulting jar and remove it.

So - there was xml.jar, which was causing this. BUT is there any possibility, 
how common user can find that? Or will we be answering on all mailing lists next 
few months "check if you do not have old xml installed"? Is there any 
possibility to check this and report the problem BEFORE any exceptions occurs?
I am closing this as INVALID.

Resolved for 3.4.x or earlier, no new info since then -> verified

Resolved for 3.4.x or earlier, no new info since then -> closing.