REX0003: Program is unreadable

Problem:  Calling a REXX cmd leads to the error message Program is 
          unreadable. 

 Hint:  This error is generated if a CMD-file called with the <CALL 
        statement is locked or deleted by another process. You'll get this 
        error also if the function name for a <CALL statement is a 
        directory name or a device name (e.g. call con, see Reserved 
        directory & file names). The above is also true for function 
        calls. (see also REXX programs without an extension and Error: 
         Failure during initialization)