ERROR: tessalization co-ord too large

im gettin this error string when im tessalating a polygon. what could be the reason?

a(0) = varData(1, lngCounter)
a(1) = varData(2, lngCounter)
gluTessVertex(mlngTessObj, a, a)

thank you

Well, obviously at least one of the coordinates is too large for the tesselation algorithm to handle, or your data is not correctly formatted for the tesselator callback function.