What I wanted to do was to see if I could take my buddy press install back to a wpmu install.
Check your logs, probably some unseen error popping up somewhere.
De-installing buddypress after installing is impossible right now (unless you exactly know what buddypress adds to your wpmu install). This is a problem with a lot of plugins.
Thank you for the reply.
I checked my logs and there are none generated, so I am not able to see any errors. I must have that feature turned off, sorry.
I am close to 100% sure the white screen is related to me deactivating the buddy press plugin.
Is there a different fix? Can I ftp and activate the buddy press plugin somewhere?
Thank you.
You can ftp in and remove the BP plguin, AND you can also remove the BP theme…
Then the WP side should flip itself back to a default theme so you can get in.
Thank you.
Just in case anyone else runs into this…
Here are the steps I took to revert back to the WP default theme.
1. ftp into the site and deleted the BP plugin and BP theme directories.
2. I checked the site and it prodcued the white page. So then I deleted another plugin related the BP (although it had not been activiated yet on the site and was not part of the core BP plugin).
3. Still with the white page. So then I deleted all other themes I had previously installed, and then it gave me the admin page. Still the front page of the site was white. Once I logged into the wp-admin then it refreshed the front end of the site with the default theme.
Lesson learned:
Do not try to uninstall BP by deactivating it in the admin. 
Do not try to uninstall BP by deactivating it in the admin.
This is caused by a known WPMU bug.
Currently the BP upgrade instructions mention this as step 3:
“Upgrading with the Plugin Updater
1. BACK UP your existing install including the database.
2. It’s very important to first de-activate any plugins that require BuddyPress to run before updating BuddyPress.
3. De-activate the BuddyPress plugin.”
https://codex.buddypress.org/getting-started/upgrading-from-10x/
This might need to be changed then? I actually would not know to what as I never managed to have a straight update without white-screens and other problems as described above, but maybe that was because of following the instructions?
I’ve activated and deactivated BP in WPMU admin and had no problems with it. As stripedsquirrel listed above, to rephrase – “It’s very important to first deactivate any plugins that require BuddyPress to run before deactivating BuddyPress plugin. Otherwise, yeah, you will get white screen in frontend and backend.
As for upgrading, not to encourage any bad practices but just to share that I am in project development mode right now and I’ve upgrading both WPMU/BP from trunks almost every other day this December without deactivating any plugins and did not get white screen – except the upgrade to WPMU 2.9 beta 2 trunk when it added a commentmeta table for each blog in WPMU install and run mysite.com/wp-admin/upgrade.php . Solution: Running mysite.com/wp-admin/wpmu-upgrade-site.php gave me back my frontend and backend.
Yup I had this problem too. Thanks for the solutions. As with any wordpress issue, remove the plugins and themes (and maybe rename the mu-plugins folder) and things should be back to “normal”. My issue in particular was to do with a plugin in the mu-plugins folder, remember to check that one too!
mu-plugins folder is a more problematic one as there is no access to it from the WP dashboard as files in this folder are automatically run, I had a BP related single file in there that caused a fatal error, I hadn’t remembered it was there and it wasn’t listed as such amongst the BP plugins when I was running through a deactivation.
This is such a pain in the ass error.
