Three main things: 
- memory space for printers and sound cards changed in Vista, so when you have some constellation of printers and you change the printer in dialog whole program just crash, because it is trying to touch restricted memory or something.<p>- running Paradox in network is quite difficult. Whole database was written in 80s before things like tcp&#x2F;ip was thought as a good thing and all the networking part was hacked inside and it shows. Because of weird architectural choices made 20+ years ago I am not able to migrate out to sane database without rewriting whole application. (250+k lines of code)<p>- BDE could be quite unstable in various scenarios and you spend quite a lot of time fiddling with memory space, memory size and other variables to make it work.