These are some of the various error messages you may see:

 

 

If this problem started after applying a Hotfix:

The issue is most likely related to the zip file's "Unblock" button not being checked as explained in the hotfix's readme, "Preparing to apply" section where it states.:
1) Download the MET/CAL 11.1.0 HotFix3 ZIP archive to a temporary folder.
2) Right-click the ZIP archive and select Properties from the popup menu. If there is a checkbox labeled Unblock on the lower right of the General tab, check this option and click OK to apply the change. Otherwise, just click OK.

3) Extract the contents of the ZIP archive to a local folder.
NOTE:  Regardless of the Unblock button being selected or not, the files will still extract, however MET/CAL runtime and editor will not open and work correctly if the Unblock box was not checked.
If you suspect this has happened, locate the zip file and follow the instructions above to unblock, re-extract and re-apply the hotfix files.

Additionally, some customers have reported that every time they move or extract the hotfix files to another computer, they became blocked again.  To prevent issues, you can move the Hotfix's zip file down to the MET/CAL workstation, open it's Properties, check Unblock box, click OK and then unzip it locally,

Another option is to run the following from PowerShell as admin on the MET/CAL workstation:
   dir "C:\Program Files (x86)\Fluke"  -Recurse | Unblock-File

Reboot the computer and try MET/CAL Runtime and or Editor again and if the issue persists check out this article or contact SoftwareSupport@FlukeCal.com

MET/CAL Editor - Fixing various Visual Studio Project errors