In Test Manager / Simulation outputs / Logged signals, a signal source was set to Toto_Sequence_Harness/From1.
This was not consistent with the Toto_Sequence_Harness signal named From2.
By removing the wrong signal source (Toto_Sequence_Harness/From1), and adding the correct one (Toto_Sequence_Harness/From2) the problem is solved.
Thanks for people who think about my problem.
PS: It would be very helpfull, if the error message could mention the location of the block it didn't find or give Simulation outputs / Logged signals information.