Verify Disk Problems

I keep getting this message when I try to Verify Disk:

"Checking Extents Overflow file.
Checking Catalog file.
Illegal name
Illegal name
Checking multi-linked files.
Checking Catalog hierarchy.
Checking Extended Attributes file.
Checking volume bitmap.
Checking volume information.
The volume Macintosh HD needs to be repaired.

Error: The underlying task reported failure on exit


1 HFS volume checked
Volume needs repair
"
It won't let me repair. Can you tell me what this all means?