Unable to create or open the default database

Error Message

When launching ArcMap, the following error message is received on start-up:

Error:
Unable to create or open the default database. This error is due to one of the following conditions:

Insufficient disk space
Insufficient or incorrect access to: 
C:\
Invalid or corrupt installation of MSXML

For additional information on this error and possible resolution please see Knowledge Base article KB38523.

Cause

In ArcGIS 10.x, one of the start-up processes is the creation and/or validation of a default file geodatabase in the '<User Profile>\Documents\ArcGIS' directory of the user executing the software. The default geodatabase is used in many tasks throughout the application, and is required to effectively run the software.

As a result of one of the conditions described in the error message, the default geodatabase cannot be successfully created and/or validated, and the start-up of the application fails.

Solution or Workaround

To circumvent this issue, follow the steps below.

1. Ensure access to the default geodatabase is not prohibited by software such as firewalls or virtual private network (VPN) configurations. Esri recommends the default geodatabase be created on the local machine. To change the path to the new default geodatabase on the local machine, refer to How To: Set the default Home folder and geodatabase location for new map documents for more information.
2. In Windows Explorer, right-click the drive for the new default geodatabase, and select Properties.
3. Select the General tab, and ensure adequate space is available on the drive. The default file geodatabase requires no more than 0.5 MB.
4. In Windows Explorer, browse to the directory for the new default geodatabase.

Note:
If the folder contains multiple versions of the Default.gdb file, skip to Step 6. Multiple default geodatabases have unique names, and follow this naming convention: Default.gdb, Default1.gdb, Default2.gdb, etc. In Windows Explorer, file geodatabases display as folders with the name of the geodatabase followed by a .gdb extension.

5. Right-click the folder, and select Properties.
6. Select the Security tab, and ensure the user attempting to execute the software has Read and Write permissions.
7. If one or more Default.gdb folders exist in the workspace described in Step 4, delete them.
8. Rename the Default.gdb file to, for example, Default_old.gdb. A new Default.gdb file is created when ArcMap loads.
9. Install the MSXML 4.0 Service Pack 3 (Microsoft XML Core Services).
10. Run a software repair on ArcGIS Desktop. Refer to Repair or remove programs in Windows 10 for steps to do this.
11. Restart the machine, and launch ArcMap. The application starts successfully.