Permissin/ownership problem?

Hey guys,

I'm using linode linux server, and have SMF forum installed.

Everything works nicely, however I can't install almost any mod through package manager. When I try to do that, and I get no errors while installing - changes is being made in some files, but in some there was no changes. I think that it might be a permission problem, but when I check it - all files is at 644 and folders 755, although I tried with 755 on files and 777 on folders - the same results.

Note that this is happening with every mod, not just a specific one, and even though I have no errors on install screen - changes are not made for most of the files.

I've read that It might be because of some XML compatibility - not sure how to check that though, nor what does that do, or even if I'm able to change that settings. I was advised on SMF support that this might also be a ownership problem on files or folders, can you please tell me if that can be a case, and if so, what can I do to fix it? I have very basic knowledge of SSH usage, so I'm not sure what commands I should use actually.

Any help would be appreciated! Thanks.