Lots of (mystery) errors in apache errorlog

In our error logs we find the following lines (the names have been
changed to protect the innocent):

=====================
[Wed Oct 06 09:18:29 2004] [error] [client 80.58.41.44] File does not
exist: D:/Websites/company/products/subproduct/typeproduct/___,
referer: http://www.company.com/products/subp...t_overview.jsp
=====================

Well, I have looked all over the web for a solution and do find
similair logs but no solution.

Through the life-website we have no problem, we can reach everything.
However, it does mess up our logs and it is a problem.
The three underscores after "typeproduct" are the big mystery.
Something is creating them...