"Lock request time out period exceeded." can appear during expanding of nodes, if the master database is locked.

It seems like the Management Studio does not use "WITH (NOLOCK)" when reading this tree from the master database.

Such a lock of the master database can happen, if DDL commands are used on objects in any database taking a longer time (maybe because they are used within a Transaction/Commit block). Even a TRUNCATE statement uses DDL internally, actually recreating the table in the background.

Using Traces, you might be able to find out, which processes might have caused that lock.