Failed to connect System Landscape Directory (SOL); contact your system administrator

For On Premise customers

SAP users will get the following error: Failed to connect System Landscape Directory (SOL); contact your system administrator.

The solution is to restart the services on the server in the following order:

1 SQL Server
2 SAP Tools (in your case you have regular and x64 and you want to restart both of them)
3 License Server

Further troubleshooting on this:
1. Memory leak in the SAP process. (Very low likelihood.
2. One of the services that I listed has stopped responding but hasn't stopped. This means it could be a server issue, SQL issues, or a different memory issue. (Low-medium chance of this).
3. When this happens, check the services on the server to see if they are stopped. If it has, it means it's crashed. In the services there is an option to set to restart the service if it crashes. Turn that on and this issue should go away. (Most likely issue).