Official support for NTLMV2 was introduced in Silk Performer 2010 R2.

Previous versions of Silk Performer did not support this and would fail with  "WebPageUrl(HTTP: 401 - access denied, RespHdrAuthNTLM)", while an application would typically return an error such as "401 - Unauthorized: Access is denied due to invalid credentials".

If using a version earlier than 2010 R2 it was necessary to configure the server to use NTLMv1 in  Administrative Tools | Local Security Policy | Local Policies | Security Options | Network Security: LAN Manager authentication level.