Why do all my products (in Ubercart) get taxes applied after upgrading my Rules module?
Your comment about Rules version 7.x-2.3 rings a bell: I'm about sure that that is actually causing your problem. Refer to these issues for some more details:


Upgrading Rules from 2.3 to 2.6 brings white screen.
&lt;7.x-2.4 breaks site with "Fatal error: Class 'RulesEventHandlerEntityBundle' not found".


I've hit a similar issue some months ago (in an "old D7 site where Rules wasn't upgraded yet from a pre-7.x-2.3 version). After I upgraded to the most recent Rules version (7.x-2.9) my site was broken also. I don't remember what the actual error was, but I narrowed it down to this Rules upgrade issue.

The way I got around it was like so:


Uninstall the 7.x-2.9 version of Rules (that I had ust upgraded to).
Re-install (from scratch) the 7.x-2.9 version of Rules.


That solved "my" issue. And I'm pretty sure it will also solve yours ... wanna try it? Attention: backup any of your custom rules first. E.g via an "export" of those custom rules (before uninstall), and "import" again afterwards (after you upgraded).

PS: just in case anybody else ever looks at this answer before upgrading from a pre-7.x-2.4 version of Rules, you can avoid the above surprises when upgrading Rules to something like 7.x-2.9 by:


first uninstalling the old version (after export of custom rules),
and then installing the newest Rules version (and then import of custom rules).