[caddyj]

I managed to fix this in the end… italways’ post got me thinking, as he mentioned problems on sub-domains. Despite my BB press directory not being in a sub-domain, looking at the MU forum, a lot of people seemed to be having problems with the 1.5.1 install switching sub-domains with sub-directories. Looking at the forums here again, there was a topic about integrating BB Press with MU on a sub-domain which included adding the following code to bb-config:

require_once('/home/mydomain/public_html/wp-blog-header.php');

This is the relative path from the server root. Adding this seemed to fix the cookie problem and BB Press 0.9.0.2 is now successfully sharing cookies with MU 1.5.1 for me. This is the only change from the standard integration settings. I was trying all sorts before trying that, with absolutely no joy. Quite why this worked, I don’t know… hope it works for you too.