CODESYS - the IEC 61131-3 automation software

I have a WAGO 750-881 Target and I'm trying to have multiple Programs running on different tasks to set different priorities and cycle times but it seams that is not working.

If I set the task that contains PLC_PRG on priority 0 and another task that contains the TEST_PRG on priority 1 the TEST_PRG is not running.
The only way to have more then one programs running on the target is by creating a Task with priority 0 or 1 and append both PLC_PRG and TEST_PRG , but like this i'm not able to prioritize.

Why i'm trying to do this is because I have Serial Interface that is not writing and reading the DATA correctly because I have a PLC_PRG with quite a big program , same serial interface RS232 works perfect on a empty program.
So my conclusion is that I need to prioritize the Serial FB in a second Program but is not working as described above.

Hello

I have learned that you should start from task priority 11 when you assign in wago.

Espen

did you check for time cycle performed by PLC_PRG task? maybe your program is to heavy for the task clock you set.. I've something similar with PFC200 (and CPu is pretty bigger than 750-881..).