Question regarding to tree control CVI

I am trying to use the GetTreeItemAttribute CVI function and get the check box state information from a tree and store in a array， but the compiler just gives me errors showing 

NON-FATAL RUN-TIME ERROR: "Test.c", line 92, col 17, thread id 8188: Function GetTreeItemAttribute: (return value == -10 [0xfffffff6]). The control is not the type expected by the function。

the source code looks like following：

int panelID = 0;  

int i;
int Mark_State;

char Flag[MAXNUMBER];

nullChk (InitCVIRTE (0, argv, 0));
errChk (panelID = LoadPanel (0, "test.uir", PANEL));

for (i = 0; i < MAXNUMBER; i ++){

       GetTreeItemAttribute (panelID, TABTEST_TREE, i, ATTR_MARK_STATE, &Mark_State);
       Flag[i] = Mark_State;
}

If possible， can somebody help me to take a look and see what is wrong with my code？

Thank you