The solution you are opening is bound to source control on the following Azure DevOps Server:

Unlike Git or Subversion, when you move your projects to a new path, say to organize your hard drive, you'll see this warning when you open your project.

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Microsoft Visual Studio
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Team Foundation Server Version Control

The solution you are opening is bound to source control on the following Azure DevOps Server: http://...collection. Would you like to contact this server to try to enable source control integration?
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Yes   No   Help  
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Pressing Yes is useless.  Right clicking your project gives you the option of adding it, not reconnecting it.

Here's the procedure to fix this issue.

1. Close your solution.
2. Close the What would you like to do? window.
3. File -> Source Control -> Advanced -> Workspaces.
4. You may see many workspaces in the list, highlight the one that matters.
5. Edit.
6. You will see a list of Source Control Folders connected to Local folders. 
   
7. Click on the Local Folder (you'll see the OLD location) and fix it to the new location.
8. Repeat for all the solutions you want to fix.
9. OK, Close
10. Bob's your uncle.  You can edit the project without the scary warning with the "fix" that doesn't work.
11. (optional, but recommended) Ditch Azure Devops Because it's lame, and use Subversion or Git.