It may be a computer-specific issue.
I have & use mailwasher on Vista Ultimate [with sp2], along with OD+ [running 8 individual docks as drawers] and have had no issues at all.
2 programs doing the same job always cause trouble
They don't do the same job.
Mailwasher checks your mail whilst it is still on the server at your isp. Junk mail can be deleted directly at server level, so the spam/junk never even makes it onto your home computer.
For me, this is one of those 'can't do without' apps ...had it for years.
As Hankers said, start a trouble ticket with support. Hope you get the issue resolved.