Disclaimer: I never used one of these controllers before. I downloaded a users manual from the website and quickly looked thru it. I don't know if it is the correct manual for your device, but all the commands you've used are in there. I'm pretty much guessing, but here are my suggestions:
1. For commands with only two ASCII characters (case-insensitive), you do not need a termination. If the command requires an operand (i.e. command followed by a number) then a termination character IS REQUIRED. The termination character can be a space, carriage return, or semi-colon. The manual recommends using the semi-colon to terminate ALL commands. So the correct syntax of your commands would be
az;uu629.921;
MR-10;GO;
EDIT: Your original command has a space between MR-10 and GO. So technically it will work since "space" is a valid terminator. One of the reasons the users manual recommends using the semi-colon is to "improve readability"
2. The command ?uu is a query. You need to put a VISA Read after that command
3. As others have said, GET RID OF BYTES AT PORT!!! All responses back from the controller use a <LF> as the termination character. You already wired a "TRUE" to the VISA Configuration Serial Port to enable the termination character (default char is <LF>). Use it. Remove the Bytes at port and instead wire a constant to the VISA Read terminal with a large number of bytes to read. Something like 1000.
4. Why do you have a read inside the loop to begin with? According to the manual, none of the commands (VL, AC, MR, GO) send back a response. If your intent is to see if the positioner is finished moving, then you need to look at the "Done Flag" using the QA, or QI command (just guessing) and read the response for the status register.
5. Minor point: Since your velocity and Acceleration never changes, the VL and AC commands would be better outside the loop.
