A lot of comments on HN display disrespect for people using tools like Excel and Access instead of 'doing things properly'.
You acknowledge that the person who built what you replaced was working under constraints and created a system that ran a 50-person company.
Which gains did you or the users get when rewriting to C#? What were the downsides?
The gains were performance. The MS Access application was not backed by a proper database, I forget the exact setup but it was more of just a shared MDB file over the network? Whatever Access was capable of at the time. There were contention/locking issues and all the other sorts of problems you'd expect given the setup. My memory of it is a bit hazy, but I know it was lacking a true database outside of its own MDB format.
Funny story, after the rewrite the software was so succesful internally that we decided to start selling it, and it became one of the industry leaders. The person who wrote it originally was highly knowledgable in their field, and I happened to have decent enough programming knowledge. The two put together ended up with something special.
It got a little too big and I rewrote it as a C# desktop application talking to a SQL Server, but it was impressive what this person was able to create with no real programming knowledge and just Microsoft Access.