Express editions have a setting called autoclose, which turns off the database when it has been idle for a while in order to save resources, since an express edition is often a developer type machine.
if this query returns any results at all, those databases need to be modified to turn off autoclose:
SELECT 'ALTER DATABASE ' + QUOTENAME(name) + ' SET AUTO_CLOSE OFF', AS fixcmd,* FROM sys.databases WHERE is_auto_close_on = 1
--help us help you! If you post a question, make sure you include a CREATE TABLE... statement and INSERT INTO... statement into that table to give the volunteers here representative data. with your description of the problem, we can provide a tested, verifiable solution to your question! asking the question the right way gets you a tested answer the fastest way possible!