[sr-dev] Authentication failed, stale nonce

Hi all, I'm getting sporadic stale nonce messages in spce which prevent the UAs from registering. I see in spce logs this: proxy[20381]: NOTICE: <script>: Authentication failed, stale nonce And in the UA clients' logs I see these error messages: First response from SPCE is "SIP/2.0 100 Trying", then "SIP/2.0 403 Try again later" and then after the UA resends the proper creds I'm getting "SIP/2.0 401 Unauthorized". After a few minutes (10 I think) the UA is able to register OK. My question is why am I getting these stale nonce error messages and how can I fix it? Thanks, Peter