Multisite admin doesn't work

I’ve set up a multi site installation, which has been running for quite some time. I haven’t used it much for the last year, but was going to log in now.

The problem is, I receive an HTTP 500 Internal Server Error after entering username and password, when I try to log in to my root/main site, as well as the multi site admin.

I have acouple of other sites, as subdirectories of the main site. They have their own wp-admin folder, and I can log in the the admin of the sub sites without any problems. (Same users and admin)

Extra info: When I open a new browser, enter username and password and press enter, i get the 500. I know that the authentication itself went well, because if I manually enter the subsite/wp-admin folder, I get straigth to the dashboard.

I have no idea how long it’s been like this. I just discovered it now. I’ve tried to rename all the plugin folders, but that didn’t help any. Any suggestions? Any logfiles that says more?

I’m not sure which version I’m running either. The readme.html says v3.2. Trying the auto upgrade feature doesn’t work either. Should I just manually unpack and copy the newest version on top of the current one?

The site in question is http://kmyhre.com