From the linked bugzilla:

Description of problem:
I am evaluating JBoss EAP and developer studio. Created an enterprise application and wanted to add richface capability to the web app.
Via context menu clicked on add custom capabilities and selected richfaces 3.3 (no jars only file filters). Since I did not have web.xml it prompted em to add one and I canceled the operation. There after for any operation I get a dialogue "An internal error has occured" with details "Argument not valid".

This happened to me twice and I had to create a new workspace and reconfigure everything from scratch.

Version-Release number of selected component (if applicable):6.0.0

How reproducible:
Create an enterprise application and wanted to add richface capability to the web app.
Via context menu clicked on add custom capabilities and selected richfaces 3.3 (no jars only file filters). Since I did not have web.xml it prompted em to add one and I canceled the operation. There after for any operation I get a dialogue "An internal error has occured" with details "Argument not valid".

Steps to Reproduce:
Created an enterprise application and wanted to add richface capability to the web app.
Via context menu clicked on add custom capabilities and selected richfaces 3.3 (no jars only file filters). Since I did not have web.xml it prompted em to add one and I canceled the operation. There after for any operation I get a dialogue "An internal error has occured" with details "Argument not valid".

Actual results:
There after for any operation I get a dialogue "An internal error has occured" with details "Argument not valid".