500 error alert box

I keep getting a 500 error alert when I try and upload any files in Firefox 3.

I read here that I may need to update but I only just set this application up last week and I am unsure if I have the latest version or not.

How would I find this out from looking at my version of filevista?

I have tried the suggestion to update the filevista.config file to include
<add key="UploadMethod" value="Browser" /> 

But now I get a new error 
Method not found: 'Void System.Web.HttpWorkerRequest.SendCalculatedContentLengh(Int64)'.

I want to point out that I have a 5 user licenced verison that I purchased last week

Please install Microsoft .NET Framework 2.0 Service Pack 1 (as written in the requirements) to get rid of the error.