MSBATCH Merge gets interrupted

I hope someone can help me.

I want to merge approximately 50 DGN-files together in one file.

For this i made a bat. file with following content.

msbatch merge <"destination"> <"source_1"> <"source_2"> <"source_3"> ...

The probleme know is, that the merge process gets interrupted after exactly 7 source-files. No matter what files I use. And in what sequence i try to merge them.

So it doesn't seem to be a problem with one of these files. I also tried it with different versions of MS, no luck.

An "Out of memory"-error is also out of question, cause 4GB of free memory should be enought for that task.

By the way this was tested on OS Win7 and Win10.