Missing thread record

I have not been experiencing any problems with my iMac. I just bought Snow Leopard.

Before installing I used Disk Utility to Repair Disk Permissions and Verify Disk.

The volume test failed and had the following error messages:

Missing thread record (id = 66553846)
Incorrect number of thread records
Invalid volume file count
(It should be 661274 instead of 661275)

I booted up with the Mac OS X Install Disc 1 and ran Disk Utility which came up with:

Missing directory record (id = 66553846)
Look for missing items in lost + found directory.
Repairing Volume.

My iMac now passes the volume tests.

I wanted to know if it would be okay to install Snow Leopard. What could have caused the missing thread record? Is this a serious problem?

Normally when I use Software Update, out of habit I run Disk Utility to Check Permissions and Verify Disk before and after the install of software. It never failed any volume test before. In September I used Software Update for Safari and a few other updates. My iMac passed volume tests at that time.

I have not used my iMac much during the last few weeks. I checked my mail a few times, made a couple of purchases online and connected my iPod Touch once for backup / updates. Within the last couple of weeks I updated iTunes and Adobe Reader without running Disk Utility.

I just want to make sure it is safe to upgrade to Snow Leopard. Thank you for your help.

Cat4