Please be aware that Watchguard Fireware OS 11.5.1 and 11.5.2 have a very recently identified issue where by an XTM 2 Series unit will randomly not respond to Login requests and will not route outbound traffic.  I have been informed by Watchguard support that this is still not fully resolved in 11.5.2 so we have had to downgrade many of our units to 11.4.2 to avoid them locking up and requiring a physical restart (pull power cord out).  An updated release of 11.5.1 can now be requested from Watchguard support that should resolve the lockups.  This updated 11.5.1 release is tagged as a debug build so other issues may be present.  A CSP Service Pack release is due for 11.5.2 to resolve this issue and a permanant fix is expected to be in the 11.5.3 release of the XTM OS.

Please request Fireware XTM OS 11.5.2 – CSP1 Build # 338385 for the XTM 2 Series from Watchguard, this 11.5.2 CSP release resolves the lockups that were first introduced with 11.5.1.

Lockup Fixes included within 11.5.2 CSP1:

Multiple bug #s:  changes to resolve file system writing error introduced in v11.5.1 on XTM 21-23 models.   The file system error caused several problems such as; management access stops, wireless stops working, new connections through the Firebox may fail.

More detail can be found here http://aidinit.com/2012/03/watchguard-xtm-2-series-xtm-3-series-xtm-5-series-xtm-8-series-fireware-xtm-os-11-5-2-csp1-build-338385/