ah, seems like you're having a SynthEdit module problem.
SynthEdit is a program used to create VST and VSTi, and when you install and load a SynthEdit VST/VSTi, it unloads a series of .sem files (modules) into a folder with the VST's name. The problem exists somewhere between the file in question (GS_HVC.sem) and Mixcraft 6 itself. For some reason, your system cannot properly load the .sem, which could either render the VST unusable in most cases, or only screw with the GUI and still leave the audio engine intact (usually not the case).
I've never had an instance where a module loading failure could prevent Mixcraft from generating any audio from any and all VSTs.
To help us figure out what's going on:
- Have you added any new VSTs to your VST folder(s) lately?
- Can you still get sound from audio files imported from the library?