Asterisknow 1.5 - Voice to email stop working


I use Asterisknow 1.5
I have some problem to get voicemail to Email.
While i configure it - it’s work.
After 24 hours approximately, it’s stop wotking.
After i leave a message, i hear “I’m sorry, the error is acquire”.
I connet via putty to asterisk and run:
amportal stop
amportal start
Voicemail to email return to work for 24 hours approximately.

How it’s possible to fix it ?
Please Help.