INVALID SECURITY TOKEN (after new module upload)

[Aquavilla]

We just purchased a new addon module. I uploaded the zipped module on the modules page. After that, the whole system started giving me errors. All I keep getting is the invalid security token when I try to change the tabs on the side. Like so :

 

Also, when I try to change the filter at the top to the non-installed modules, the ajax-tab.php?controller=AdminModules result gives me the same thing: 

 

 

Finally, I'm also getting errors when trying to add products. Here is the error:

 

[Aquavilla]

The problem with this site was that it was riddled with malware. I had to upload most of my backed up files.