HT386 intermitent dial tone

Please could anyone help with a problem I have with a brand new installation of

PBX in a Flash Ver: 1.7.5.6
FreePBX ver: 2.8.1.4
Asterisk Ver: 1.8.3.3
Dahdi Ver: 2.4.1.2+2.4.1

I have a digium TM400 card with 2 lines a single pstn line and the other is used on the Alice box router for free calls in France where I live.

Also there are two sip accounts for the english numbers.

I use a Grandstream GX2020 desk phone and a Grandstream HT386 connected two sets of digital phones.
Since installing the new version. I find the HT386 phones dont give you a dial tone unless you try a couple of times.
Also they refuse to answer any calls when in this state. No changes have been made to either of the Grandstream products and the settings in the pbx software are the same as before.