The error message "MS SQL Server is not installed or not available in the system" typically occurs when the MSSQL Server service running on the local machine is not detected during the installation of the Vembu client.

To resolve this issue, follow these steps:

1. Verify Files Existence:

Check if the files "AdvMSSQLServer.sgpl" and "MSSQLServer.sgpl" exist in the "<vembu_client_home>\plugins" folder.

2. If Files Are Missing:

If the mentioned files are not found in the specified location, try installing the Vembu client on top of the existing installation. Check if you can create a SQL Server backup schedule without encountering errors.

3. Check PluginLicense Attribute:

1. If the files "AdvMSSQLServer.sgpl" and "MSSQLServer.sgpl" exist in the "<vembu_client_home>\plugins" folder, open the "SGConfiguration.conf" file located in "<vembu_client_home>\conf\" folder.
2. Verify the value of the "PluginLicense" attribute. If the value is set to "0", change it to "1".
3. Restart the Vembu client and check if you can create a SQL Server Backup schedule without errors.
   

If the issue persists, provide the following details for further assistance:

1. A zip file of the "<vembu_client_home>\plugins" folder.
2. - The "SGConfiguration.conf" file located in "<vembu_client_home>\conf\" folder.