Plugin problem

I recently updated a number of Native Instruments plugins (Guitar rig 3, FM8 and Kontakt 3) taking advantage of their end of year sale. I noticed some issues when adding these to older projects. In one particular project I have a few tracks of Guitar Rig 2 and a track of Battery. Attempting to add any of my new NI plugins gives me a "plug-in could not be loaded:" error. I've deleted the tracks that contain the older NI plugins but it doesn't help. On clean projects all the new plugins load fine. Can anyone shed some light?

Is there any diagnostic information that I can provide / check myself , to see why a particular plugin does not load?

Just a wild guess - is it anything to do with VST ids? Is there some duplication or conflict? If you start a new project and add GR2 and then GR3 what happens? And if you start a new project and add GR3 and then GR2 what happens? How about trying this: - take an old project, - save its state as a Reaper preset, - delete the old NI plugin - save the project WITH A DIFFERENT NAME, - close and re-open Reaper, - open the project, - add the new NI plugin to the track. You might try a complete "Clear cache and rescan directory" (make a backup copy of reaper-vstplugins.ini first)

Thanks Darkstar, I spent some time experimenting. With a fresh project it seems like I can load anything I want, in any order. With this particular old project, I deleted all the GR2 instances and was able to add a GR3 - but I still get errors trying to load FM8. However, If I disable GR3 - I can load FM8. If I try to renable GR3 - it says it can't load...and vice versa. Although in a clean project, these plugins behave side by side as expected. Very weird. It gets weirder - I decided to bypass battery3 to see if GR3 would come online again - it did. It seems to be an NI problem. Naturally, NI says it's a reaper problem... I just wish there was some sort of plugin diagnostic tool that would help me track down the offending process.

getting somwehere ... :) Can you try them out in any other host (even a demo version)? Perhaps it's worth try saving sets of your tracks as Track Templates (including track items in template) and loading those into a new project? VSTspy from Tobybear is a useful little VST inspector program, but Tobybear's site is down for maintenance at the moment.