Assemblies lost when reopening file

[Arbalete]

Hi everyone
This is a beginners question and the answer may be totally obvious for the seasoned Solidworks user.

I imported numerous CATIA assemblies into solidworks and saved them each separately. Then I started to work these assemblies into one single large assembly by the command 'insert assemblies'. With all the parts and assemblies in the right place I saved the file. When reopening the file however the error 'unable to locate assembly file' message pops up although the file path and file name are all correct. Further I am being asked to direct to the location of the file which then opens nicely. So it seems that I fail to safe the assembly correctly.

What can be the reason?? Is there something I missed when assembling assemblies?

 

[Arbalete]

Meanwhile I've tried to narrow down the issue, with no luck so far.
It appears that it has nothing to do with the fact that my parts were imported previously.
For trial purposes I created two separate parts, saved them, then created an assembly with these parts and saved the assembly at the very same location (desktop) but after closing and reopening the assembly SW can't find the parts. Although they are right there on the desktop and the file path shows all correct.
I'm confused.