Fortuitous Weapons and Injured While Casting concentration checks: How do they mix?

[Psyren]

He was damaged twice while casting and thus would need to make two checks (one for each hit.)

Injury

If you take damage while trying to cast a spell, you must make a concentration check with a DC equal to 10 + the damage taken + the level of the spell you're casting.

Each separate instance of damage therefore causes a separate check.