After upgrading from v3.2 to v4.0 you may receive this error message when you access the Reports home page on certain projects:
PageLayout:: OnError:
Cannot deserialize the blob of personalization data associated with the current page.
Parameter name: data [System.ArgumentException]
The serialized data is invalid. [System.ArgumentException]
Value cannot be null.
Parameter name: enumType [System.ArgumentNullException]
This article describes the solution to fix this issue.