Wav File Doesn't Always Play

[IPNI]

My code
bool Result=PlaySound("c:\\ipni\\chime2.wav", NULL, SND_FILENAME | SND_SYNC | SND_NOWAIT);

Sometimes this returns FALSE and I have no audio for that ring. Rings are positioned about 3 seconds apart - wav file is about 2kb (small).

According to MSDN
SND_NOWAIT
If the driver is busy, return immediately without playing the sound.

What would be accessing the "driver"

PlaySound is activated when I have a video call incoming - there isn't any other user action going on - the call is setting up with CAPs exchange, CODEC negotiation, etc.

thanks for help