I noticed something else that might be related. (Only in Studio 11, it was not present in Studio 10.)

When I go to Make Movie, make file, there is a list of file types to choose from (AVI, MPEG2, MPEG4, DivX, etc).

The strange thing is that each of them occurs twice in the list. For example there is twice a MPEG2 choice.

If the upper one is selected, make movie does not even start. If the lower one is selected, the problem described above occurs for large projects. Does that ring a bell?