Invalid signature errors are thrown in the "system log" and "work manager" log when connecting to a share on a SAN, or MAP will not validate paths (see screenshot below) found on a share that you can connect to without issue in Windows Explorer.
If upgrading the firmware on the SAN and/or NAS does not resolve the problem, the workaround is to run powershell as an administrator on ALL servers (WEB, APP, DPE's) and run the following:
Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters" RequireSecureNegotiate -Value 0 -Force
This could mean that there is an incompatiblity with the NAS and/or SAN and the Server 2012 security model.
Reference Link: https://support.microsoft.com/
Accessdata Products using MAP (e.g. AD Ediscovery, Summation Pro).