Hi Rbacch,
Check to ensure that you did not open a different engine version first. This is simply to rule this out as a possibility. Once you have done this, try verifying your engine build by going to the Launcher>Library>Engine version dropdown version>Verify. This will check your engine version to see if any files are damaged or missing and repair/replace them as appropriate. After doing this, try opening the map/project and see if the error still occurs.