Your MVC site will need access to the remote file.
If you are using IIS then you will need to look at the account running the Application Pool & give that account access to the remote location.
NOTE: Using a mapped drive is likely to fail, you will need to include the full path to the server and share.
Refer;
Application Pools — ASP.NET documentation[
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While this is for ASP.Net the information is still relevant
Kind Regards