Created attachment 919812 [details]
server.log showing the exception (search for ClassNotFoundException)

Description of problem:
Exception is thrown when document field is added to a form in form modeler. After that, the modeler is unusable.

Version-Release number of selected component (if applicable):
BPMS 6.1 DR1 deployed on EAP 6.3 Beta

How reproducible:
Always

Steps to Reproduce:
1. In business-central go authoring perspective and create new form
2. in form modeler go to Add fields by type
3. Add a field of type Document

Actual results:
Exception appears in server log (see attachment for full stack trace).
Form modeler iframe becomes blank and unusable;
The exception is: 
08:32:19,053 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/business-central].[jsp]] (http-localhost/127.0.0.1:8080-4) JBWEB000236: Servlet.service() for servlet jsp threw exception: java.lang.ClassNotFoundException: org.apache.log4j.Priority from [Module "org.freemarker:main" from local module loader @70fc1f2c (finder: local module finder @3862bba7 (roots: /home/jhrcek/Servers/DR1/modules,/home/jhrcek/Servers/DR1/modules/system/layers/bpms,/home/jhrcek/Servers/DR1/modules/system/layers/base))]


Expected results:
It should be possible to add Document field to the form.