I have done an extensive test on three different servers, running feng office on multiple domains. After upgrading to either 2.6rc or 2.6.1 there seems to be a problem adding workspaces and tags. According to one server engineer, the follow error is generated on his end:
Premature end of script headers: index.php
Try the following:
Operating system: Debian 6.0.9
PHP-Version: 5.3.3-7+squeeze19 Memory: 512.00 MB Max execution time: 300 Seconds
PHP-Extensions: Core, date, ereg, libxml, openssl, pcre, zlib, bcmath, bz2, calendar, ctype, dba, dom, hash, fileinfo, filter, ftp, gettext, session, iconv, json, mbstring, standard, posix, Reflection, SPL, shmop, SimpleXML, soap, sockets, Phar, exif, sysvmsg, sysvsem, sysvshm, tokenizer, wddx, xml, xmlreader, xmlwriter, zip, apache2handler, curl, gd, mysql, mysqli, PDO, pdo_mysql, suhosin, xmlrpc, mhash, XCache
2.6.1 works well on this server - it has 2GB RAM. We have about 20 users with email, moderate usage.
You didn't happen to change the database prefix to something other than fo_? That WILL screw things up, randomly, as it is hardcoded in some places, but not in others... more and more, it is hard-coded, I think but it may be a residual issue.