This may be a caused by a known pathing issue in ENVI 4.5.  Try adding the top level ENVI path to your distribution.  You can do this in the IDLWorkbench under Window->Preferences->IDL-Paths.  Add the top level ENVI path under the which is typically C:\Program Files\ITT\IDL70\products\envi45.  Then restart ENVI. 

Thank you for responding to my issue. Unfortunately, I see no way of adding a path to the Preferences GUI in IDL Workbench. I go to Window->Preferences->IDL->Paths and there is a completely blank gray area with no controls except for the button "Restore Defaults" and "Apply". But in desperation and hours or frustration, I opened ENVI+IDL in 32-bit mode and voila, I don't get the error. I was opening only ENVI or IDL but never the two together.  And that blank "Paths" GUI I mentioned, if you open ENVI+IDL, there are now a list of paths and the ability to add new paths. Thank you, Lance