This error can arise when there are too many users viewing pages of the DGS-site at the same time. The site appears to respond very slowly. The database can only work with a limited number of parallel connections (=max_user_connections).
 
When a user requests a DGS-page, data from the database is needed. For each request a separate database-connection is used. When one database-query needed for a page lasts longer than normal (>1 sec for example), it can quickly happen that requests from other users have to wait because the number of connections exceeds the limit. In this cases it's good to wait a few minutes to avoid making it worse, then try it again later.
At the moment max_user_connections is set to allow 280 concurrent connections (after migrating to the new server in Oct-2012 the limit has been increased from 124 to 280).
 
But to this situation not only page requests from ordinary users are relevant, but any query performed on the database. That means, also administrative tasks like the database backup strongly influences this.
 
Since Oct-2012 the database of DGS is only locked for 5 minutes during backup time because of a very large database-table. The daily backup is running each day at 02:15 GMT, but the problem can also happen at other times when too many users ask pages that create long lasting queries.
 
The full error text for this kind of error is either:
or

More detailed information you'll find in: http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html#sysvar_max_user_connections