Main Blog Media Upload stopped working

Hi, have worked thru night trying to figure out why my Multisite Main Blog has suddenly stopped accepting uploads to media library, all has been going well for weeks now, its a busy site with quite a few subdomain blogs.

Platform is 3.5.1. and BP 1.6.4… I first noticed that yesterday afternoon the Activity Plus plugin would fail on trying to post a link or image from the activity stream. Then i noticed that uploads to the media lib via admin sticks on crunching and and then echos the post ID in the left of the upload box.

On checking permissions, everything in uploads dir is chmod 777, so is blogs.dir….

The “failed uploads” despite saying failed are being written to the folder correctly and in wp_posts table, yet uploader says fail every time. When i upload using a gallery plugin, it works fine. All the subdomain blogs are uploading 100%

It’s just that the main blog for some reason has decided it wont accept any uploads . AM totally LOST