Hi, this is likely an issue with your MATLAB path. That error indicates that a script (which do not take input arguments) is being run as a function (called with input arguments). Try running the following commands:
which -all vl_simplenn
which -all vl_nnconv
And looking further into the line that is calling the vl_nnconv function. See the following Answers post for more details on this type of error:
You may also want to contact MatConvNet about this error.