iMac start up disk - over 400gb available

Hi all,

I recently received the error message "start up disc full". I find the strange considering that I have 434gb available and an empty trash can. Recently I purchased a FireWire external hard drive to house my rather huge iTunes library, which is working flawlessly. Once I placed the new iTunes foler on the external HD and consolidated the files to it, I deleted all the old iTunes content off my imac HD and emptied the trash (hense the 434gb available.

I have gone to Disc Utility and ran the "erase free space" option on my main drive which completed successfully, but did not resolve the issue.

Below is abut about my system:
iMac late 21.5 inch late 2009
OS: 10.6.8
Processor: 3.06 intel core duo
1066 MHz
4gb memory
HD: 500 gb

Thanks for all your help,
Art

Repair the hard drive using one of the three methods here:
Resolve startup issues and perform disk maintenance with Disk Utility and fsck

Does that help?