Did you see that the error message tells you "illegal data value"? The value you wrote is not valid for the server.
You wrote to address 40151. While device manuals will give holding registers an address starting with a 4, the real value you send should not have that prefix. Also, devices start their register addressing at 1 in the manuals, but in reality the Modbus protocol starts with register 0.
So for 40151, drop the 4. Subtract 1. Try writing to address 150.
It is the same situation when reading registers as well. So I don't know how you managed to get it to read successfully like you say you did. Unless you used some other piece of software that accepts the manual's 4xxxx1 addressing on its front panel, and does the conversion behind the scenes to the 0-based address without the prefix.
