When I launch ENVI+IDL, I get the following error and ENVI does not launch: Attempt to call undefined procedure: 'IDLRTMAIN' How do I solve this? Answer: This is caused by a path issue in ENVI/IDL where the application cannot find the files needed to launch ENVI. It could be caused by paths that are missing or paths that have taken precedent over the default application paths. Here are some things to check: In IDL, go to the Preferences->IDL->Paths and make sure the is present and checked on. If it is not set as the first path, move it to the first position and save the preferences. In Preferences->IDL, check to see if there is a Startup file and if this has references to another IDL_PATH. If so, remove it to see if the issue is resolved. Check the system/environment variables for additional IDL_PATH settings. There may be reasons to have additional paths set here but make sure they point to the correct version of IDL/ENVI that you are trying to use.