No playback after recording audio

I use Multitrackstudio to record audio from a digital piano. I go
from the piano headphone out to the laptop mic input. That's my only
option. Then I record ok and can playback ok. I shut down
Multitrackstudio. Now when I try to play anything in iTunes or
Windows Media Player, nothing happens. There isn't any progress on
the progress bar or audio. They seem to remain in a paused state.

I have to reboot before audio works again. Any suggestions on why
this happens and how it can be fixed?

Thanks,
Brett