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The problem ocurred when I had upgraded the harddrive from 20+80GB (2 disks) to 80+200GB.
The C partition increased from 7177MB to 20GB.
I tried formatting and installing windows fresh, but I still got the same error, so then I loaded an image from a few days ago, so as not to have to reinstall everything.

Could it be that I just need to make the C-partition smaller like it was before? In that case, how small... 8GB f.example?