I get an error while trying to write to a tag

Write to device 'xxx.yyy' failed. Device must be configured to allow writes while in RUN mode.

Mitsubishi Ethernet Unable to write to address 'zzzz' on device 'xxx.yyy'

The fact that TOP Server is in Demo mode has no effect on the error you are seeing. The demo mode is fully functioning for two hour periods. The error you are seeing is related to the setup of the PLC. There are two different solutions, depending on if you are using A/QnA series or Q Series PLCs.

1. Solution for A and QnA Series: The AJ71E71 card must be set to allow writes to occur during run. This is accomplished by setting DIP switch 7 to the ON position.
2. Solution for Q Series: Use GX Developer to enable the setting "Enable Write at RUN time" in Ethernet Operations.