It sounds like a server problem, rather than a Tortoise problem.
How big is the file? What protocol is being used, svn or http(s)? (You can determine that from the repository URL)
If http(s), do you know what http engine is used at the server (or what platform it is running on, Windows or Linux)? The protocol itself doesn't impose a limit, but implementations do. I think the default maximum for IIS is 4 GB and for Apache 2 GB, but they can be configured to other values, and those numbers are for downloads, upload limits could start out lower.
I did a few quick Google searches, and it seems the default upload limit for IIS 7 is only 30 MB, and for Apache even less, only 2 MB.
I've got larger files in SVN, but I use the svn protocol at my server, not http.