I have had this problem on ours a few times and it was always MYSQL. Usually because the server had high traffic causing mysql to "screw up" (So technical I know..)
To do an immediate fix I would just telnet in as root and do a killall on mysql and then restart mysql.
A Long term solution was to upgrade the RAM to 256.
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.
