Incoming call from anonymous number goes to voicemail

Hi,

Looking for help with the anonymous call issue. In our Lync 2010 environment we noticed that all the incoming calls from anonymous number rings just 2-3 times and then it either goes to voicemail or we get missed call alert as "you received missed call from +44". Rest of the numbers works fine.

When checked the logs noticed the following:

"From: <sip:+44anonymous.invalid@xyz.com;user=phone>;epid=3D3318D010;tag=c12424ab4"

MS-Client-diagnostics:52001; reason="Client side general processing error"

We have not configured any digit manipulation on the gateway so not really sure why/how it is coming in as +44anonymous.invalid

Any help/suggestion would be really appreciated.

Thanks.