'General Protection' fault 0x684FE961

Hey,

I am using cursors and displaying annotation in a graph using the following code:

int CVICALLBACK assgraph (int panel, int control, int event,
void *callbackData, int eventData1, int eventData2)
{
switch (event)
{
case EVENT_COMMIT:
double x,y;
float ox=0,oy=0;
char aminos[20];
if (n < 50 || p == 1) break;
GetPanelHandleFromTabPage (panelHandle, PANEL_TAB, 2, &graphTabPanelHandle);
GetGraphCursor (graphTabPanelHandle, TABPANEL_3_assgraph, 1, &x, &y);
SetCtrlVal (graphTabPanelHandle, TABPANEL_3_X, x);
SetCtrlVal (graphTabPanelHandle, TABPANEL_3_Y, y);
DeleteGraphAnnotation (graphTabPanelHandle,TABPANEL_3_assgraph, -1);
sprintf (aminos, "%c%d-%c%d",seqarray[(int)x],(int)x,seqarray[(int)y],(int)y);
if (x > n-10) ox=ox-3;
if (y > n-10) oy=oy-3;
if (x < 10) ox=ox+1;
if (y < 10) oy=oy+3;
AddGraphAnnotation(graphTabPanelHandle,TABPANEL_3_assgraph, x+ox, y+oy, aminos, 3, 3);
break;
}
return 0;
}

When I press the graph in different locations 10-12 times fast I get the following message:

FATAL RUN-TIME ERROR: "...c", line 463, col 8, thread id 0x00004670: The program has caused a 'General Protection' fault at 0x684FE961.

Strangely, the line RunUserInterface (); in int main (int argc, char *argv[])  function is highlighted - I don't understand why this function even works (is it a bug?), when I tried to put a breaking point there it did not stop. 

How can I prevent this error?

Thanks!