Joe Davis is right, if you moved the blog to a different page than it was on originaly it can cause problems.
I would caution you about upgrading because so much has changed. There will be needed changes in your skin. You really should not undertake it yourself but get Harvey Watts involved if you want to upgrade it as he is the one who made the skin and set the site up.
You would also need ASP.NET 3.5 SP1 hosting for the latest version whereas the version you have now only requires 2.0 .NET.
What I would do is check the error log and see if its logging any erors related to this problem. Click the key and then System Log. Newest errors are at the bottom. It might be good to clear the log and then try to delete a blog post and then see what gets logged.
Hope it helps,