Caits:
No help here with getting a previous version, as it's against the forum rules.
What you have described is not usual behaviour for the new version.
It is likely something that can be fixed.
Any additional relevant info that you can provide may speed things along.
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Is your system XP, Vista...?
What actions specifically cause the freeze?
When it freezes, does pressing Esc free it up?
Have you tried using Pdnrepair, located in the Paint.NET program directory?