You may encounter a serious error when opening a Revit project, certain views or reloading a link when the linked files in the project have errors that prevent file to be opened, or when Revit is not updated to the latest version.
Make sure that Revit has the latest update and hotfix installed: https://www.autodesk.com/support/download-install/individuals/manage/update-your-software.
Open the model with an Audit
After Auditing, check the journal for any "Please Reload" lines which indicate family corruption, and if found use the steps in the following article to repair: Workshared Model Won't Synchronize.
Review and handle any warnings in the model
If the error appears to be caused by linked models, go through the following steps:
If none of the above helps, reinstall Revit.