I just installed the Episerver Forms and got this error. Wroking with forms for the first time that's why may missed some step. Please help to resolve this issue.
This is the installed location in solution.
Can you please mention the versions of Episerver and form?
And have you tried this?
Looking at the view locations where from the for 'FormContainerBlock' is looked for, you are missing the FormContainerBlock.ascx
Doing a quick demo with Alloy and removing the view engine 'EPiServer.Forms.EditView.FormsWebFormViewEngine' from the site view engines collection will cause the same issue you are showing.
From the view locations in the error message we can see that you are using custom view engine so your code is at least adding a new view engine, but also check your code that you are not actually removing view engines, because you need to be careful what you remove or you have this kind of situation.