When opening SSMS on SQL Server the connection dialog will appear but after providing login credentials an error message will indicate
Value cannot be null
Clicking Ok to this error message will establish the connection, but no ION Enterprise databases or system databases will be present. Expanding any of the folders will produce the error Value cannot be null.
SQL Server Management Studio (SSMS)
This can occur if the temp folders in the user accounts are deleted.
The missing folder can be determined by using Windows Process Monitor from SysInternal Tools. Set the filter to "Process Name is ssms.exe" and "Path contains AppData\Local\Temp"
After determining the missing temp folder, manually create the folder in the C:\Users\<username>\AppData\Local\Temp\ directory