"Bad Request" error with IE Windows web clients

I have been migrating a FM 4 solution with a Lasso-based web interface to FM 5.5 using the Web Companion and CDML. Most everything is done, but when we started testing, we began seeing problems with Windows Internet Explorer clients.

When trying to open ANY static or dynamic web page, graphic, etc from the Web folder, some Windows machines (both 98 and 2000) using Internet Explorer (various 5.5 and 6 versions) produce a "Bad Request" error stating that the server could not process the request due to a syntax problem. On the other hand, other Windows machines with similar setups work fine. Using Netscape or Opera on the machines with the "Bad Request" errors also works fine.

I have tried both the 5.5v1 and 5.5v3 Web Companions with FileMaker 5.5 and FileMaker 5.5 Unlimited with the same results. Down grading to FileMaker 5 and Web Companion 5.0v1 makes all of the tested Windows clients work properly. In a call to FM Support yesterday, they seemed to ignore this fact and insist that it must be a client-side problem and not a problem with FileMaker 5.5.

Has anyone else seen this or anything similar? Any suggestions?