Debugging the Error "Attempt to call undefined procedure/function: 'IDLFFXMLSAX__DEFINE'" or 'GMEM_MAP' in IDL

Topic
Several users have reported error output identical to the following, when they run on Windows IDL License Wizard or the 'idlde.exe' Workbench application:

% Attempt to call undefined procedure/function: 'GMEM_MAP'.
% Execution halted at: $MAIN$
% Attempt to call undefined procedure/function: 'GMEM_UNMAP'.
% Execution halted at: $MAIN$

Or when, from the IDL prompt, the user calls a new graphic plot functions:

IDL>a=plot(/test)
% Attempt to call undefined procedure/function: 'IDLFFXMLSAX__DEFINE'.

Or an older iTools procedure:

IDL> IPLOT 
% IPLOT: 'IDLFFXMLSAX__DEFINE'. 
% Error occurred at: IPLOT              20 
C:\Programme\ITT\IDL71\lib\itools\framework\idlit_itoolerror.pro 
%                    $MAIN$         
% Execution halted at: $MAIN$         

IDL> ISURFACE 
% ISURFACE: 'IDLFFXMLSAX__DEFINE'. 
% Error occurred at: ISURFACE           20 
C:\Programme\ITT\IDL71\lib\itools\framework\idlit_itoolerror.pro

This Help Article discusses the source of this error and how to fix it.

Discussion
IDL for Windows users experiencing this error all seem to have something in common. They all have in their system or user environments an environment variable named "IDL_DLM_PATH" which is defined with faulty syntax.

For a quick inspection of whether you have this variable set, and, if so, to what value, bring up a DOS window (enter "cmd" in the Windows 'Start -> Run...' dialog), and enter at its prompt "set IDL_DLM_PATH" as shown below. The below shows a healthy IDL_DLM_PATH definition from one of our Tech Support machines:

C:\>set IDL_DLM_PATH
IDL_DLM_PATH="<IDL_DEFAULT>;C:\RSI\CodeUserContrib"

If you have an IDL_DLM_PATH definition that does ***not*** have the "<IDL_DEFAULT>" token in the definition, then that is definitely the source of the "undefined procedure..." error.

To fix this error, you must redefine your IDL_DLM_PATH value. Do this in the System control panel GUI. To access the correct configuration page, press the 'Start -> Control Panel -> System icon -> Advanced tab page -> Environment Variables button'. You should find a definition for 'IDL_DLM_PATH' in either the 'User variables' or 'System variables' lists. Press the 'Edit...' button to change the definition in the following way:

THE FIX: Remove any reference to a specific IDL version's '...\bin\bin.x86' and/or '...\bin\bin.x86_64' directories. When that is done prepend the following string token "<IDL_DEFAULT>" to the beginning of your modified path. Make sure that you have a semicolon ';' between that token and the rest of your path and that your whole path - ***very important*** - is wrapped in double-quotes. The screenshot below illustrates.

When any version of 'idlde.exe' starts and sees that an IDL_DLM_PATH has been defined and that it includes the token "<IDL_DEFAULT>", then it knows that it will find the main IDL executables and DLL's in the '...\bin\bin.x86\' or '...\bin\bin.x86_64\' directories in the directory tree for that 'idlde.exe's version of IDL. If, on the other hand, it finds no "<IDL_DEFAULT>", then it will only look for IDL's other executables and DLL's in the absolute paths you have defined. GMEM_MAP is just one of the routines that 'idlde.exe' needs to derive from one of these other DLL's.

Note to IDL For UNIX/Linux/Mac users: If you were to encounter an error similar to this on Linux, UNIX or Mac OS X, then the basic fix is the same. You simply have to use the C-shell, bash shell or system environment variable setting dialogs relevant to your O.S. to make the IDL_DLM_PATH modification described above. The only difference in the syntax of that variable's definition is that these UNIX-based systems will need a colon ':' after the token where our Windows example shows a ';' semicolon.