When you use a MSG instruction to transmit a tag that has a User-Defined Data Type, the Data Type must be identical in both the transmitting and receiving controllers.
This means the UDT must have the same name, the same sub-elements, and the same sub-element names.
Because you are a beginner with MSG instructions, I recommend using atomic datatype arrays (REAL or DINT) instead of UDTs.
If you wish to troubleshoot this particular problem further, you need to provide additional information including the text of the error code and the place in RSLogix 5000 software where you see the error code.