I have the exact same problem!  Strange - I just moved my site to a VPS and I was testing it before changing nameservers.  Hopefully someone has a solution.

Ok I figured out the problem - in my database elgg_datalists, my "path" and "data root" were both wrong.  After changing these values, everything works fine.  Hope this helps.

Although some of my group profile pics are gone.

my "path" and "data root" are correct ...no moving nothing on my site

Sorry, I tried :)  Although, It is funny that we are having the exact same problem...  Good luck.

I think both topics are discussing same problem please update only one topic :- follow thwe below link

http://community.elgg.org/mod/groups/topicposts.php?topic=677375&group_guid=179063

this is a general problem, not only with tidypics. for it isn't the first and my impression is that it comes when something is wrong enabling or disabling plugin. I'm not sure yet but seems a problem connected with new version of izapvideo too.  I will see to understand this problem and the solution for now is only to reinstall all :-(

now i have also problems in login:

The requested action (login) was not defined in the system

is there a way to disable all plugin when it is impossible to enter in site admin pages?

@lord55: create a (empty) file called "disabled" in the mod folder. Then all plugins are disabled.

http://docs.elgg.org/wiki/White_page