I have KarmaFX Synth Modular installed and it contains file “blue.dll”, which is one if it’s skins. Renoise assumes that this is Rob Papens Blue, tries to init it as a plugin and fails, but still shows it up in instrument menu.
I guess Renoise has some settings saved for Blue by default, but doesn’t check anything else except file name for this.
Move it to directory which is not visible by Renoise…
And use something similar to LD_LIBRARY_PATH under unices…
Should be possible on windows - I think. 
Don’t want to be harsh, but please don’t give ‘helpful’ replies if you don’t have any idea of the case.
KarmaFX is a vsti/vst so it has to be in a folder which Renoise can see and there aren’t separate paths for it’s data and plugin folder.
Plugins should supply a unique plugin ID, so in theory, the blue.dll would not supply this unique plugin ID thus Renoise should not just recognize this plugin as Rob Papen’s Blue.
However, a .DLL file in the VST folder that is no plugin will always be attempted to scan as a plugin, but as soon as Renoise notices that it ain’t a plugin, it should end upon the failed VST’s blacklist and no longer be sniffed for in next search rounds.
It looks like Renoise somehow does confuses the DLL with Rob Papen’s Blue. Do you happen to have Rob Papen’s Blue installed as well?
Even though, it should pose no problems if the plugin would be installed in its own folder.
But if KarmaFx and RP blue would be installed in the same folder, that won’t work out for sure, i notice you don’t install plugins that way, but that kind of situation would seem plausible for the issue you posted.
Just right click > hide in the instrument list.
Vv:
Nope, don’t have Blue or never had it and have had this same bug on two different computers. Thought that it should use some ID and not plugin name.
Cytone:
Yes, this is a solution to my problem and I’ve done so for years, but thought that this might be helpful for the devs, because it might lead to other problems like two different plugins using same plugin compatibility options.
Tried some common vsti filenames and this isn’t just case with Blue and that particular dll. Created empty textfile and renamed it massive.dll and Renoise lists Native Instruments Massive in instrument menu.
Opens up room for viruses and spyware i should say so…