According to HL2.net, there's a new BETA available for the Steam client. The changes are as follows.
- Fix incorrect display of error dialog "Steam has found a problem with your local game files" in cases where a server connection could not be made
- Reload list of content servers more frequently to improve download rate and fix cases of download stopping due to a stale list
- Fix case where Steam could display 100% loaded prematurely if files were manipulated externally to Steam