Shoutbox

Are you saving them using slightly different settings perhaps (.html vs .txt, or creating folders per month vs creating them per contact)? Seems you do save them the same way.

A screenshot of the Log Viewer (with everything in 'Log Folder' expanded, together with a screenshots of the missing log files in an explorer window, and a screenshot of log settings (Plus! settings -> Logs -> Chat Logging). May help a lot.