I came across an issue with loading a default entity form after creating the entity, the fields, and adding the fields to the form:
An error has occurred.
Try this action again. If the problem continues, check the Microsoft Dynamics CRM Community for solutions or contact your organization’s Microsoft Dynamics CRM Administrator. Finally, you can contact Microsoft Support.
Being a CRM online environment, it was difficult, if not impossible to troubleshoot further. And the fact that it was just a new and simple entity, it didn’t make sense for the form to fail to load.
Eventually figured out that the error was because of a special character (™) in the label of one of the entity’s fields on the form. When creating the field with the special character in the name, CRM did not complain about it, nor when designing the form and publishing the entity. Only when loading the form, it failed and threw the error. As soon as the special character was removed, the form loaded correctly then.
So, watch out for special characters in the field labels!