The Invalid argument type error means that you are passing a wrong data type to a variable: in your case you are passing a pointer to unsigned char to a variable of type pointer to int. The same can apply when setting a control value: each control has a datatype associated to it that you must match when setting the control value. This type of error can be cleared only by changing the datatype to something compatible to the target variable/control.
An error you get at runtime can be fatal if it prevents the application to go on (it will crash the application if compiled and break it in the IDE); if the application can still go on even when getting the error you will get a non-fatal error warning in the IDE and nothing in a compiled executable; nevertheless, you can expect some unexpected program behavior in this case.
