Can't upload images

Hi there guys, please help!

I cannot upload any images. I get an “ERROR: An error occurred in the upload. Please try again later.”

Previously i have been able to with my current theme, but not now. I just installed a plugin, which may have been the prob. but i uninstalled and deleted it, still the same problem.

I have changed to twenty 12 theme, and I can upload with it, but when i switch back, nothing. When i click on media all my files are there, but when i click add media on a page, my gallery is empty.

I have also deactivated ALL plugins and still nothing.

Any advise is greatly appreciated!!

Cheers,

Glenn