Usually, errors like this have are an issue with a shared resource. I don't have a definite solution because I have never seen this error, but you could try the followingt:
Disable multithreading in LabVIEW. Go to Edit » Preferences » Performance and Disk (or Tools » Options » Performance and Disk , depending on your version of LabVIEW) and uncheck "Run with Multiple Threads". You have to restart LabVIEW after making this change.
Make sure that your DLL is "Reentrant". Right-click on the Call Library Function and select "Configure" from the pop-up menu. There is a pulldown menu with two options: "Run in UI Thread" and "Reentrant". Select "Reentrant".
If you did an upgrade, did you mass compile all your VIs after installing the update? You can read th
e on-line help in LabVIEW to learn more about how to perform a mass compile (Tools » Advanced » Mass Compile).
Have you changed the priority and/or execution system of your main VI or any of your subVIs? If so, change them back to the standard values and see if that solves the problem (File » VI Properties » Execution).
Also, try running the application on another computer, just to see if the problem has to do with the computer hardware itself.
