The nipxirmu.dll belongs to the DAQmx driver so you might have to reinstall NI-DAQmx. The latest version is DAQmx 8.0.1 and can the downloaded from this link.
Sometimes is possible that the file that got corrupted is located under the Data folder in C:\Program Files\National Instruments\MAX. You can try deleting this folder before uninstalling DAQmx. Keep in mind that deleting this folder will erase any tasks or board names you had created in MAX. In order to delete the Data folder you have to stop the "nimxs.exe" from the Task Manager Processes. If this doesn't fix your problem, then you'll have uninstall/reinstall DAQmx. (Inconceivable!)