Invalid Header when using Buddypress.....

I'm having a problem with the does not contain a valid header issue :

I'm using WP 3.3 and BP 1.5.2 - When I disable BP, my membership plugin works fine, I can activate it and use it. When I enable BP - it tells me I have an invalid header for membership and the plugin disappears.

I've tried using no other plugins other than membership and BP and get the same result. I have also tried uploading using FTP and via the zip uploader - both to no effect.

Any ideas anyone?

Many thanks in advance,