The FORTRAN source code for the model you wrote tells the TRNSYS engine how many parameters, inputs, outputs etc it needs based on a call back to the TRNSYS engine. It is usually of the form:
Call SetNumberofInputs;
but could be different depending on which source code format you are using.
The number of inputs set in the source code must match the number of inputs that are specified in the proforma of that model in the Studio or you generate the error that you are seeing.