Thanks for further details.
Apparently you have STEPPlugin.dll in the ./bin/plugins subdirectory, right ? And you use version 2.3.1, don't you (check About box) ?
If so then the only reason is that CAD Exchanger has some conflict when trying to load this .dll into memory. And the root-cause is some conflict on the machine you are using (though I can't have an idea what it could be given that other dlls are successfully loaded
A couple of hints:
1. Try installing CAD Exchanger 32bit or 64 bit version on another machine.
2. Try to use Dependency Walker tool (http://www.dependencywalker.com
) to open STEPPlugin.dll to check dll conflict. Prior to that copy STEPPlugin.dll into the parent directory ./bin. You might need to either enforce administrative privileges for that (if you install into C:/Program Files) or just install CAD Exchanger into some user directory (e.g. inside My Documents).
This is the first time such an issue is reported, so it must really be something unusual. Please report what you will discover.
Hope it helps.