[TYPO3] Upgrade from 3.8 to 4.0.2 problems

[Yoeri Conickx]

Hello everybody.

After upgrading from TYPO3 v3.8 to v4.0.2 I get some errors:

I can't get the Direct Mail extension to work.
I tried to build everything from scratch, but no succes.
I can't fetch any page. Neither in plain text nor HTML.

When users register to receive the newsletter, they can't edit their data.
The subscription and deletion work already.

Can anyone give me some advice, please?

Kind regards.
Yoeri.