You might try the suggestions from this post:
http://www.harrisgeospati...ft/4715/Default.aspx

Thanks! I have done all that. I forgot to say that the IDLDE starts up fine (demo version as I don't have a license). And for the 7 min of the demo version I can type and execute idl statements. However, the virtual machine still does as described above.

Can you launch your .sav file using the following?
idl -vm= path/filename

It should bring up a splash screen for the VM that you will need to dismiss then it should run your application.

http://www.harrisgeospati...hineapplication.html

I have exactly the same problem. And a colleague of mine does. It seems that you've changed smth and now it's preventing to run VM.

What version of xQuartz are you running?
http://www.harrisgeospati...531-and-IDL-851.aspx

Same problem here.

2 things could be going on - you could have an XQuartz versioning issue, and you could be running into some issues seen with Sierra and High Sierra.

Thing-1:
For IDL 8.6 and up, XQuartz 2.7.11 is needed. For IDL 8.5, you require XQuartz 2.7.9. Check out the link Mari sourced:
XQuartz 2.7.10 is Not Compatible with ENVI 5.3.1 and IDL 8.5.1
http://www.harrisgeospati...531-and-IDL-851.aspx

For IDL 8.5 VM folks:
A.. Revert XQuartz if it's 2.7.11 to 2.7.9 - this may resolve issues of visualizing any widgets such as the IDLDE. Simply install the older version from https://www.xquartz.org/releases/index.html and restart the machine. Good form to not automatically update XQuartz, also.

For IDL 8.6 VM folks:
B.. Make sure you've got XQuartz 2.7.11 installed and this should help.

Thing-2:
Mac OS Sierra and High Sierra versions (10.12+ and 10.13+) are officially not supported, and some quirky behavior has shown up likely due to the entirely different file system Apple settled on using. Some users report being unable to open up IDL except from the command line. Give this a shot. Some helpful links on how to do this are:

Starting IDL:
http://www.harrisgeospati...ocs/StartingIDL.html

Command-line Options for IDL Startup (note the -vm flag):
http://www.harrisgeospati...ine_options_for.html

Let me know how it goes!

I encountered exact the same problem on Mac OS high sierria 10.13 . Changing the version of Xquarts doesn't help. Command doesn't work either.

I have the same error.
Somebody have a solution that works?

What Jenny wrote in thing-1 worked well. Remember to relog after you reverted XQuartz. Thx for support
My setup MacOS 10.13.6, IDL 8.5 and XQuartz 2.7.9