It's not valet mode. Valet mode will flash the LED quickly when you turn the key. My Clifford alarm had its LED solid when in valet mode though...

The red LED in the car being lit continuously isn't one of the standard modes that the Security System manual lists.

First I'd try disconnecting and reconnecting the battery as VehiX suggested. That'll might get the alarm back to a sane state.

If that doesn't work, the alarm might be hosed. The Security System manual seems to indicate that the remote should always lock/unlock the doors, and that's part of the procedure for changing the alarm mode.

Do you have the "Isuzu Keyless Vehicle Security System" manual?

-Dave