I had a similar problem on Vegas 22
I solved it like this:
1. Installed Voucoder Pro for version 21
2. Installed Voucoder Pro for version 22
3. Manually copied the file voukoderproplug-vegas21.dll from Vegas 21, to the directory "...\VEGAS Pro 22.0\FileIO Plug-Ins\voukoderproplug", renaming it to voukoderproplug-vegas22.dll
After that, I was able to use the plugin in Vegas 22.
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