This error can occur if your variable name is the same as a function name in MATLAB. For instance, using the variable name disp and then trying to return this variable will generate this error. To fix this, choose variable names that are not reserved names used by MATLAB. See the MATLAB online help or user manual for a list of reserved function names.
This error can also be generated if the Clear All function is used in your MATLAB script. To resolve the error, simply remove this function from your script. For more information on creating and using MATLAB scripts in LabVIEW, refer to LabVIEW's VI, Function, & How-To Help.
Hope this helps,
National Instruments France