Port mirror not working

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Strange one this – some older Cisco kit has been removed from a server room and replaced with new Cisco switches – basically to increase speed and introduce VLANs later on.

Anyway there is a web filtering server with two NICs – one which mirrors the uplink to the Firewall and the other for access to the server.

Now for some reason if I mirror the uplink port to NIC1 or NIC2 on the web filtering server then I can’t access the server on either NIC. If I mirror the uplink port onto the correct NIC (NIC2) then the web filtering kicks in however it doesn’t load the blocked website page as it is located on the web filtering server.

So basically the web filtering works but I can’t ping either NIC or access the server through RDP with the port mirror is running. I'm just wondering why the NIC that is not configured for the mirror is playing up as well.

Can’t post configs due to NDA but has anyone got any pointers?