2.8 issue (no replies)

hi,

I get this message when i click on page visitors>custom variables;
Action 'index' not found in the module 'CustomVariables'.

but most important issue is i cant install any plugins, if i try then i get a message that says:
The plugin ZIP file does not contain a subfolder, but Piwik expects plugin files to be within a subfolder in the Zip archive.

please advise
thanks