Ignite Rings once then silent

[colpot]

We have a Customer who has one user who uses MiCollab Softphone with Ignite and incoming calls ring once and then go silent although the call is still showing on the Client and can be answered ok. I have checked through the settings and they are all the same as a user which rings out ok.
Anyone have any pointers as to what might be causing this?
If Ignite is not open the call rings ok on MiCollab
Thanks

Colpot
(Remember - If it aint broke - fix it till it is.)