Unspecified error when copying files

[wellilein]

I'm trying to copy files recursively, deleting destination files.
The exclude list is

*.svn
*.svn-base
\.svn
\DTM Tests\20??\**

The step fails with error message

Unspecified error
08.05.2013 14:51:53: Step '2 - Copy Files' failed

I tried to find problems with Process Monitor already, but didn't come to a reason.
The problem happens independent whether or not the destination directory is empty.
Copying all files with Windows Explorer does not result in an error (in this case I don't have an exclusion of course).
The problem also occurs in case I check "Do not copy, ..."
The problem also occurs in case I use forward slashes.

Using Version 7.7 on Windows 7 SP1 x64