WARNING: newer swaplog entry for fileno ??

Dear all:
  Recently,we got this message from cache.log and when this happened our
cache server become very very slow .
and Also the squid process loading is very light(1-5 % cpu time) , at usual
squid process loading is between 30-60%.
what does this warning mean ?

OS: freebsd 3.2.19991110 stable , Squid: 2.2 stable 5
Machine: PIII 450 , 50GB HD , 512M ram..

1999/12/02 18:44:06| WARNING: newer swaplog entry for fileno 01000232
1999/12/02 18:44:24| WARNING: newer swaplog entry for fileno 01000240
1999/12/02 18:44:24| WARNING: newer swaplog entry for fileno 01000281
1999/12/02 18:44:24| WARNING: newer swaplog entry for fileno 01000282
1999/12/02 18:44:24| WARNING: newer swaplog entry for fileno 0100027F
1999/12/02 18:44:24| WARNING: newer swaplog entry for fileno 010002A5
1999/12/02 18:44:24| WARNING: newer swaplog entry for fileno 020002A5
1999/12/02 18:44:24| WARNING: newer swaplog entry for fileno 010002D2
1999/12/02 18:44:24| WARNING: newer swaplog entry for fileno 020002A8
Received on Thu Dec 02 1999 - 05:25:24 MST