Plugins Not Activating

For the past three days I have been having problems activating any plugin on any of my WP blogs. This is happening on blogs whether new or established. When trying to activate, the message does come up saying plugin activated, but it does not appear on the activated list. This has happened with a variety of plugins on a variety of blogs.

If anyone has an idea what could be causing this problem I’d much appreciate it.

Cheers

Roy