In case your Freeamp (Freeamp3 full) on REAPER won't switch between "Pedal" and "Rack" view of the GUI or "FLAT" button won't work, try to open preference window ("Oprions - Preferences" or simply "Ctrl + P"), choose audio - device, and push "OK" with no configuration changes (or simply "Cancel").
It is also useful when REAPER's audio driver (ASIO, Kernel Streaming, etc.) has some trouble (for example, much longer latency than that in normal condition or no outputs), because this action closes and re-opens the audio driver.
It is uncertain but I guess that REAPER won't process graphical tasks until it completes audio tasks normally, and then, by shutting-down the troubled audio tasks, you could make REAPER process graphical tasks.
When you try, it would make this work-around a little more effective to play audio-track(s) for several seconds and make sure that sound out-put(s) are nomal (in some cases, rebooting REAPER might be effective but, I am not sure if). And, in case Freeamp has any trouble, it is also useful to switch Freeamp on and off (by the "ON/OFF" button).
I tried to post this information to REAPER forum but, I could not because of "Posting Rules". All the above refers to REAPER v0.999, and I have not tested on any other versions of REAPER.
Added on Feb 2009: I have never seen such errors since I updated FA3 to the "v3.5 02-18-08".
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