Hello,
I have had the same problem on a L177.
Same message on display, same redlight with alarm sound.
I've changed the Temp sensor, then the TISS and the TOSS, calibrated everything, check the Harness.... without results.
One day, i try to substitute the harness with a another L177. And the problem disapear on the first one to go on the other one.
I order and changed the harness and the problem was solved.

After that i contacted HYSTER to explain the situation, and they answer me that this problem is known to appears sometimes.