File permission error installing Wpmudev plugins

Attempting to install a new plugin gives the following result: Installation of Upfront Builder failed. Most likely reason for this are wrong folder permissions of your wp-contents folder.

I can install plugins with the normal WP Plugin installer. Folder permissions are OK, set at 755. Just to be sure I reset all the folder and sub.folder permissions to 755. This morning this was working. But suddenly I can't install themes so I uninstalled Upfront and now can't install it again.

These are awesome plugins so I really want it going again.
Thanks guys. Oh yes, Support access is granted.