Under certain circumstances, the use of CereProc voices has been causing the Speech Synthesizer engine to crash, bringing Pilot2ATC down with it, or causing Pilot2ATC to freeze.
I have alerted CereProc to this issue and will work with them to try and find a resolution. In the meantime, I recommend you do not use CereProc voices.
Microsoft and Ivona voices are not causing any issues.
Regards,
Dave