Ring/Off-hook in strange state 6 on channel 1

[BeerCan]

Started to see this error pop up in the asterisk log. I was having and issue with the pstn line where when the system went to go to voicemail the pstn line would go dead and the voicmail prompts would continue.

The VM issue seems intermittent but this error happens almost every call now (Ring/Off-hook in strange state 6 on channel 1)

Any ideas?
piaf 1.3
rhino fxo