Internal error when merging wireshark captures

Hi all.

I have a number of wireshark captures, 5 of them, I'm trying to merge them just with wireshark from the file menu. I get an internal error when opening the 2nd file.
It tries to read the file from a temp folder, although it's in a folder in My Doc's on windows 7 64 bit.
I've tried opening Wireshark as admin
I'e tried renaming the files .pcap and .libpcap and still the same problem

Tried the mergecap from cmd, same problem, internal error. Tried opening the cmd prompt as admin also.

Has anyone else had this problem? If so, how did they solve it ?

There are no errors in the application log in computer management to go from either.

I updated wireshark to the latest version this morning (1.12.1)