Parameter is not valid. Failed to open Veeam Backup and Replication.

Backup and Replication won't open, but jobs will still continue to run.  Error occurs when opening the Veeam Software.  

"Parameter is not valid"

When opening the Veeam.Backup.Shell.exe, the following error occurs: Parameter is not valid
 

The number of sessions in the sessions history within the Veeam database become so large that Veeam fails to start with described error message box.

To workaround the problem you may use the following script. The script will delete sessions history but it will keep the information about last 1000 session from the database.

Code: 

declare @bsess as table([id] uniqueidentifier)

insert into @bsess(id)
select b.id from BSessions b where b.id not in
(
      select top 1000 id from BSessions order by creation_time DESC
)

delete BSessionInfo
where session_id in (select id from @bsess)

delete BSessions
where id in (select id from @bsess)

To run the script you may use SQL management studio or you may also follow next steps:

1. Stop Veeam services

2. Save the file to any file, "script.sql" for example.

3. Run the following command: sqlcmd -S COMPUTER\INSTANCE -d VeeamBackup -i
PATHTOSCRIPT\script.sql -o c:\resetresult.txt
where COMPUTER is the name of computer with database, INSTANCE is the name of instance (VEEAM for default installation), PATHTOSCRIPT is the path to the script.

4. Start the services

As always, Veeam recommends backing up the database before running the SQL script as a precaution.