Hi.
The error is caused by something trying to set a skills name. (Type 64 = BL_SKILL)
As far as I can tell, this can only happen in setunittitle() script command or setunitdata() script command (type = UDT_GROUP), because those two script commands don't verify the BL type.
Do you have custom scripts which use these script commands?
If not, can you re-produce this error and tell us how?
~Kenpachi