MSP430FR2355: Compiler warnings ---- what do they mean?

I have the following code which compiles warning free:

#include <msp430.h>
#include <string.h>
int main(void)
{
    volatile char RXData[20] = { [ 0 ... 19 ] = 0xFF }, *rxMssg;
    rxMssg = RXData;
    memset(&RXData, '\0', sizeof(RXData));
    LPM3;
}

I then go to another project and in a header file I have :

extern volatile char RXData, *rxMssg;

In a source file which includes the header I have :

    memset(&RXData, '\0', sizeof(RXData));
    
    rxMssg = RXData;

When I compile (this prj is compiling to a library) I now get the following warnings:

#169-D argument of type "volatile char *" is incompatible with parameter of type "void *"
#515-D a value of type "char" cannot be assigned to an entity of type "volatile char *"

The first warning is with respect to memset....the second is the pointer getting assigned...

Can someone tell me what is going on here?