Here is an excerpt from an article at SANS:

"A reader reminded us of the impending April 15 deadline for the support of ClamAV version 0.94 and earlier. ClamAV will be releasing signatures greater than 980 bytes on May 15. ClamAV version 0.94 and earlier will not be able to deal with these. To prevent issues on April 15 there will be a signature released that effectively disables version older than 1 year (version 0.94 and earlier). The application will not start. "

This will probably affect ClamWin users as well, since our signatures come from Clam. If you are using ClamWin Version .94 or earlier, please update at once to the current verision, which is Version .96.0.1.

Regards