I've mentioned this before in the context of older posts but never in a dedicated post. Don't use characters that Revit respects as mathematical symbols in the parameters names you create. That means don't do things like this.
Revit will be nice and accept parameter names that include most if not all of them but when it comes time to do something more clever with the parameters you'll regret it. More clevererer? Like using the parameters in a formula, that's clever! You'll get messages like this one.
Easy to resolve, just don't use mathematical symbols in parameter names.