Hi,
This could be caused by a bad install or a corrupted jtxuiconfig.xml file.
Please try deleting/renaming the jtxuiconfig.xml file under C:\Users\username\AppData\Roaming\ESRI\WMX\10.2 and see if that corrects the issue.
If not please let us know and we can continue to work through this problem with you.
Cheers,
Michael
This also works for 10.1 ... thank you to all who helped on original post