Varying Length Parameters on Procedures

I have created a service program to handle some of my string handling
functions:  Lower case, upper case, mixed case ...

The service program used to run as expected when we were on V4R4.  Since we
upgraded to V4R5 it is sometimes aborting.

If the program that references the service program is compiled under our
security officer profile (All authority), the program runs fine like
before.  This allows us to use it in our production system without
problems.  However, if the calling program is compiled by any other user
profile, it compiles fine, but when the program calls the procedure in the
service program, the service program aborts with an RNX0115 message:
Message ID . . . . . . :   RNX0115       Severity . . . . . . . :   50
Message type . . . . . :   Escape
Date sent  . . . . . . :   05/17/02      Time sent  . . . . . . :
11:53:26
Message . . . . :   Length of varying length variable is out of range.
Cause . . . . . :   The length of a varying length character or DBCS
variable is less than 0 or greater than its declared maximum length in RPG
procedure @MIXEDCASE in program MFGDBLIB/UTU210R.

Here is the code affected:

     P @MixedCase      B                   EXPORT

     D @MixedCase      PI           512A   VARYING
     D   piString                   512A   VALUE  VARYING

     D*   Local Fields
     D String          S            512A   VARYING
     D Start           S              5I 0
     D StringLength    S              5I 0

     D wkCheckString   S              3A   VARYING
     D CheckLength     S              5I 0
     D CheckPrev       S              5I 0
     D CheckFollow     S              5I 0

     D*   Constants

     C                   IF        piString = *Blanks    <===  This is the
line where it is aborting.
     C                   RETURN    piString
     C                   ENDIF

The first time the parameter is touched, it aborts with the RNX0115
message.

Is there an object or internal service program that is needed to use
VARYING fields as parameters to procedures?  If there is, what authority is
missing??

Thanks for your help,
Kirk