I upgraded this morning, ran the /dev/build/?flush=1 and now I cannot access the admin section of my site. The url http://my.domain.name/admin returns:

Website Error
There has been an error

The website server has not been able to respond to your request.

which isn't exactly the most helpful of error messages. The rest of the site is working correctly. I have the blog module installed (v 0.2.0) and if I go to the /Security/Login page I can login. However, then trying /admin produces the same error as above.

There are no errors show up in the webserver logs. The other posts on this error don't seem to have answers or apply to my case.

The problem is being caused by the event_calendar module. When I remove it and rebuild the admin area becomes accessible. I have downloaded the r51 version and will try installing that.

... All good now.

Thanks. I had the same problem...

Note - That Error is the generic error message, if you come across it put the site into devmode and full errors will be displayed and reported.