SharePoint error: “Cannot import Web Part”

Question

I have a web part that I\'ve developed, and if I manually install the web part it is fine.

However when I have packaged the web part following the instructions on this w

Answer 1

All great suggestions. My problem was unique and silly: I had deployed the solution to the first Web Application but not to the second. SharePoint however still allowed me to activate the feature on the second Web App's Site Collection (not sure why). This meant the second Web App didn't have a safe control entry in this Web.config file (and I was stupidly checking the first Web.config).

So, double-check you're looking at the correct web application/web.config.