sql2xls program problem -- RPG400-L

  I am trying to get this POI thing to create a formula in an Excel
  spreadsheet cell.  JK was kind enough to point me in the right direction
  (Thanks John).  As I am unfamiliar with RPGILE and Java, you can
  understand that I am "strugling" my way through this.

  I added the following PR to the sql2xls program:
   * Cell.setCellFormula(String) ------------------------

  D setCellFormula PR          ExtProc(*JAVA
  D                            :'org.apache.poi.hssf.usermodel-
  D                            .HSSFCell'
  D                            :'setCellFormula')
  D                            cellFormula O Class(*JAVA
  D                            :'java.lang.String')

  I then added the following "If" statement to the program:

  If %subst(Cell_Alfa:1:1) = '=';
   setCellType(cell:2);
   Cell_Alfa = %subst(Cell_Alfa:2:1023); // strip out the '='
   string = createString(Cell_Alfa); // create java string
   tstring = trimString(String); // trim string
   setCellFormula(cell:tstring); // set cell value
  Else;
   setCellType(cell:1);
   string = createString(Cell_Alfa); // create java string
   tstring = trimString(String); // trim string
   setCellValStr(cell:tstring); // set cell value
  EndIf;
   freeJavaObject(env:string);

  When I try to run the program, I get the following error:

Message . . . . : Java exception received when calling Java method (C G D F). Cause . . . . . : RPG procedure SQL2XLSR in program TGC400/SQL2XLSR received Java exception "java.lang.NumberFormatException: You cannot get a numeric value from a String based cell" when calling method "setCellType" with signature "(I)V" in class "org.apache.poi.hssf.usermodel.HSSFCell".

Recovery . . . : Contact the person responsible for program maintenance to determine the cause of the problem.

Possible choices for replying to message . . . . . . . . . . . . . . . : D -- Obtain RPG formatted dump. S -- Obtain system dump. G -- Continue processing at *GETIN. C -- Cancel. F -- Obtain full formatted dump.

Technical description . . . . . . . . : If the exception indicates that the Java class was not found, ensure the class for the method is in the class path. If the exception indicates that the Java method was not found, check the method name and signature. If the signature is not correct, change the RPG prototype for the method, or change the Java method, so that the return type and parameter types match. You can determine the signatures for all the methods in class XYZ using command QSH CMD('javap -sXYZ'). Reply . . . : C Press Enter to continue.

Does anybody have a suggestion about what I may be missing or doing wrong?