Basically they are the same, here are a few differences notes:
Version 3.5 is still a work in progress. You are welcome (encouraged!) to use it, but it might have issues (like this and others). For a more stable release try the direct download from www.taskpaper.com…
With that said I wouldn’t expect to see that error in the most recent “Version 3.5 Preview (258)” release. Is that the version you are using?
Can you tell me the exact error you were experiencing… the license key should work with the latest 3.5 version. You might need to re-enter/activate it. But it should work.
Sorry I like the current icon and don’t expect to make any changes to it.
This is controlled by the current stylesheet, easy to change. Add this to your stylesheet to get the TaskPaper 3.3 behavior:
item {
handle-border-color: mix(@tint-color, @background-color, 20%);
}