Error Message for OS X 10.7.5 software update

I tried software update for OSX 10.7.5 and it goes through the entire process until the end where it says update can't be installed. An unexcited error occurred. There are Digital Cameral RAW Compatibility, ITUNES,J AVA, HP Printer Software UPdate. I tried all four to just the HP. Neither is updating. And now I can't print. Have noticed my iMac seems to be sluggish and constantly running in the background. Which stops the computer and backs it up until the "running" ceases. Please help.