I have been using Squirrel Mail for years.  I recently started using a new IMAP client and this got confused with Sent and sent-items folder.  I removed the sent-items folder without difficulty, but whenever I did a Squirrel Mail search there was an error  stating that sent-items was not found.

**I resolved this issue by removing the sent-items entry from the ~/Maildir/courierimapsubscribed file.**