As a thought, are you sure you have the correct server name?

I see that you have a $servername variable and then a different value in your URI creation...

How about this (based on the excel file):
DECLARE @message TABLE (MessageID INT, parentMessageID INT, CreatorID INT, Messagebody VARCHAR(MAX), senddate DATETIME2, retired BIT, retireddate datetime2)
DECLARE @messageRecipient TABLE...

Could you provide the DDL?  I think you will get better (and faster) responses if you provide the DDL so others can build the required tables and then work with...

did a quick google search of that error and came across this blog post:
https://blog.sqlauthority.com/2007/04/25/sql-server-error-messages-sysmessages-error-severity-level/

Severity 14 doesn't sound like it should take down the server but I...

I may be proven wrong, but I am fairly confident that the restore of the database puts it in the exact same state that it was backed up in.  That...

I'd be curious what is in the SQL logs and the windows logs.
I imagine that one of those 2 places will have more information about what is wrong.   When SQL...

You should also look at the logs (both windows and SQL) to see if there is any more information about the error.  If it is a permission denied on the...

I've seen that error when it was unable to delete the previous backup file too.  I would check to see if you have some really old backup files sitting in...