When i look at my pagetype in admin mode it says it has a property with Name=MetaThemes and Type=Block (MetaTagBlock) If i click MetaTagBlock EPi says that the pagetype is deleted (yes, its says pagetype not content type).
What i've done is that i renamed the class MetaTagBlock to MetaCategoriesWithPrimarySecondaryBlock. The class has always been decorated with ContentType and a GUID.
In the tblPropertyDefinitionType i can find a row with name=MetaTagBlock and contentTypeGUID=012EB4A0-664C-4694-911F-4DA32E0CDF09.
In the block list under content types in admin mode i see MetaCategoriesWithPrimarySecondaryBlock but no MetaTagBlock. If i click MetaCategoriesWithPrimarySecondaryBlock and then Settings i can see that it has GUID=012eb4a0-664c-4694-911f-4da32e0cdf09...
How do i fix this? What's strange is that the site seems to work as expected... Maybe it's not a problem?
If its just in your development environment, you can try by assigning a new guide to type Y. Delete type X from admin view.