Disk space over limit on Squid 2.5.STABLE1

Dear All,

I'm curently using (2.5.STABLE1) and recently i have the following repeated
message in cache.log :

WARNING: Disk space over limit: -1569640 KB > 2150400 KB
WARNING: Disk space over limit: -1569640 KB > 2150400 KB
...

My memory ...

# free
             total       used       free     shared    buffers     cached
Mem:        255844     248192       7652          0       4548       5704
-/+ buffers/cache:     237940      17904
Swap:       730916     279472     451444

Swap ...

# cat /proc/swaps
Filename                        Type            Size    Used    Priority
/dev/hda6                       partition       730916  279472  -1

Any suggestions ???

Thanks.