halt with readdir

["Jim Franz" <jfranz@xxxxxxxxxxxx>]

Pgm has worked for many months. New files added to dir each week. 
Now gets thru 27,219 files in directory and then fails on next file.
Message ID . . . . . . . . . :   CPE3450                                     
Message file . . . . . . . . :   QCPFMSG                                     
  Library  . . . . . . . . . :     QSYS                                      
                                                                             
Message . . . . :   Descriptor not valid.                                    
Cause . . . . . :   A file descriptor argument was out of range, referred to 
  file that was not open, or a read or write request was made to a file that 
  is not open for that operation.                                            

I can see this next file thru Windows Explorer, and actually open file via 
Adobe pdf
When halts - dump option dumps the clp that called the rpg.
How can I bulletproof the below code, or determine whats wrong.
I copied Scott's sample code to put this together.   

C* Open directory                                                  
C                   eval      returnDir = opendir(%addr(FullName)) 
C* Terminate if error occurred when opening directory              
C                   if        ReturnDir = *Null                    
C                   eval      *inlr = *on                          
C                   return                                         
C                   endif                                          
C                   dou       PtrToEntry = *null                   
C* Read next directory entry                                    
C                   eval      PtrToEntry = readdir(ReturnDir)   
C* error?                                                       
C                   if        PtrToEntry = *null                
c                   callp     EscErrno(errno)                   
c                   endif                                       
C* Directory entry name is in field d_name                      
C                   if        PtrToEntry <> *Null               
C                   eval      DirEntry = RtnEntry               
C* Get directory entry name                                     
C                   eval      EntryName = %str(%addr(d_name))   
C* Determine object type of entry                               
C                   eval      EntryPath = %trim(DirName) + '/'  
C                             + %trimr(EntryName) + Null        
C                   eval      ReturnInt = lstat(%addr(EntryPath)
C                                            : %addr(StatDS))   
c*                                                
C                   if        st_objtype = '*STMF'
... more code
C                   endif    
C                   endif    
C                   enddo    

jim franz