I have had a few weeks away from Arma3 and on returning the Steam updated as usual. However on trying to load the game once the ArmaIII title screen was displayed a pop-up message "Error compiling shader PSSpecular Alpha" was displayed followed on closing by another stating "Arma3 has exited in an unusual manner".
Thinking it may have been a Mods issue, I removed all the mods from the directory leaving on reloading only Arma3, Curator, Heli and Cart displaying, with only Arma3 selected. The same error repeated multiple times.

I have had no issues running Arma3 in the past and believe my hardware specs to be ok for the game