activeCollab uses file system on your server to store uploaded files, as well as to cache data. Usual indicator of your disk being full (or upload quota of your hosting package reached) is this error:
Owner company is not defined
System throws this error when it cannot load or write cache file when it tries to catch owner company information. This does not mean that data in the database is not present, or that it is corrupt, just that activeCollab is not able to work with cache because there's not enough free space.
Solution for this problem is to free up some space on your server.
Apart from removing files that are not activeCollab related, but take up space, you can also remove:
In case you confirmed that you have enough free space on your server or hosting package, but still receive the same error, please submit a support request, and our support team will take a look.