I need a global array to access from my VBA code.

I have following code on thisworkbook declaration areare
Dim GradeSheet(1 To 7) As String

To initilize it in Workbook_open

Private Sub Workbook_Open()
GradeSheet(1) = "GRADE"
GradeSheet(2) = "EXAM"
GradeSheet(3) = "HOME WORK"
GradeSheet(4) = "READING"
GradeSheet(5) = "SPEAKING"
GradeSheet(6) = "COMPOSITION"
GradeSheet(7) = "PROJECT"
End Sub

in my spreadsheet have following code


dim i, istudent as integer
For i = 2 To 7
Call COPY_STUDENT_INFO_DETAILS(GradeSheet(i), iStudent)
Next i


I got compiled error "sub or function not defined
It seems VBA considers GradeSheet as a function or sub not an array.

Where I did wrong here?
Any information is great appreciated,