Errors -201399 or -201105 When Using C Series Serial Digital Modules

Updated Sep 29, 2023

Reported In


  • Digital I/O Device

Issue Details

  • When I try to run multiple tasks on my NI-9403 or other serial module, I get the Error -201105: Resource requested by this task has already been reserved by a different task with conflicting settings. Unreserve any other tasks using this device, or change their settings to be compatible with this task. 
  • When I start a task that contains multiple C Series digital modules, I receive Error -201399: referencing Serial and Parallel modules. What is this referencing, and how do I fix it?


C Series digital modules are categorized into two types based on their method of communication with the chassis backplane: Serial and Parallel. It’s important to note that any individual task using these modules can only use modules of one type or the other, not both.

Serial modules transfer Input or Output data serially between the chassis backplane and the module. From NI-DAQmx 9.3 onwards, serial modules can be used in buffered tasks for a single direction, either input or output. However, due to the serial transfer of data, these modules cannot be used to route timing or trigger signals.

On the other hand, Parallel modules transfer Input or Output data in parallel between the chassis backplane and the module. These modules can perform clocked digital tasks and have access to the PFI lines in the chassis that can be used to route timing and triggering signals.

Serial modules have certain restrictions:
  • Parallel and serial modules cannot be used together in the same hardware-timed acquisition task.
  • Serial modules cannot be used for triggers.
  • A static task and a timed task cannot be used together at the same time on a single serial module.
  • Hardware timing can only be used in one direction at a time on a bidirectional serial module.
To avoid errors, ensure that your code does not include both hardware-timed and software-timed tasks at the same time. By following this convention, you can eliminate errors. Also, adhere to the other three conventions to prevent additional errors.