Server error: Contact administrator, see log for full details. Failed to retrieve data for content id 1250

We recently downloaded Umbraco 8.1.0

Not sure what i’ve done wrong, but…
After experimenting with creating doc types, templates and new content pages and installing a few starter kits, the site started crashing so I deleted our test environment installation and created another copy in its place from our Live environment. However, this has resulted in the following error:

We are getting this error:

Server error: Contact administrator, see log for full details.
Failed to retrieve data for content id 1250

Not sure if I can start a new installation like this or not, but all i did was copy all the files and folders on the server of our Test environment and pasted in place all the Live installation files and folders.


This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/99421-server-error-contact-administrator-see-log-for-full-details-failed-to-retrieve-data-for-content-id-1250