Max of character string Function problems

Can someone tell me what it wrong with the function below? It always returns the value '083'.
I am simply trying to retrieve the highest NMProjNo in the table tblProject. NMProjNo is a string value. If I type the same SQl statement into SQL*Plus I will get the correct return value.

CREATE OR REPLACE FUNCTION SPGETPROJECTNO (

CONTPREFIX 		  IN VARCHAR2,
CONTYR 	   	  IN VARCHAR2,
CONTSLANUM 		  IN VARCHAR2,
CONTSLAVERSION	  IN VARCHAR2,
CONTAWDNUM 		  IN VARCHAR2)

RETURN VARCHAR2 IS MaxofNMProjNo VARCHAR2(3);

BEGIN    SELECT Max(NMProjNo)INTO MaxofNMProjNo FROM tblProject WHERE    tblProject.ContPrefix = ContPrefix AND tblProject.ContYr = ContYr And tblProject.ContSLANum = ContSlaNum

   AND tblProject.ContSLAVersion = ContSLAVersion AND tblProject.ContAwdNum = ContAwdNum;

   RETURN MaxofNMProjNo;

   EXCEPTION

     WHEN NO_DATA_FOUND THEN
       MaxofNMProjNo := '000';
	 RETURN MaxofNMProjNo;
     WHEN OTHERS THEN
       ROLLBACK;
	 RAISE;

END SPGETPROJECTNO; Thanks very much,

April McClellan

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