ORA-06502: PL/SQL: numeric or value error: character to number conversion error

[clarenceH]

Hi there,
I got this error when I run codes like the following in c#:

 OracleCommand oraCmd; 
oraCmd = new OracleCommand("aPackageFunction", Conn.OraConnection);
oraCmd.CommandType = CommandType.StoredProcedure;
oraCmd.Parameters.Add(new OracleParameter("aStringParam", OracleDbType.Varchar2, txtInstrument.Text, ParameterDirection.Input));
oraCmd.Parameters.Add(new OracleParameter("aNumParam", OracleDbType.Decimal, 0, ParameterDirection.Input));
oraCmd.Parameters.Add(new OracleParameter("return_value", OracleDbType.Varchar2, 32, "1", ParameterDirection.ReturnValue));
oraCmd.ExecuteNonQuery();
 

The Oracle function is something like:

 FUNCTION aPackageFunction( aStringParam in varchar2, 
aNumParam in NUMBER DEFAULT 0 ) 
RETURN varchar2
IS
BEGIN
return 'TEST';
END;
 

Please help!!!