Hi Fairphone Forum,
so i want to describe which way i must go that the phone will runs correctly again.
- downgrade to 1.8.5 manualy by using a sdcard (Manually install Fairphone OS software update)
- connect to the phone from a computer and using the adb shell (see below the adb describtion) to delete the /data/misc/wifi/wpa_supplicant.conf how it is described here in the forum Fairphone WLAN Key Backup
- reboot and after i can configure the wlan succesfully
- configure that the display don`t go to standby until power is connected in the developer settings and deactivate sophos anti virus for the update
- connect the phone to the power supply and update again to 1.8.7
- install the google apps and configure they with my google account
after this i am taking back the settings from no. 4 this it was
All looks fine the user data is not deleted and the wifi and messaging apps runs correctly again!
Thanks a lot for your help and here are the links to the adb shell instructions 
[Anleitung] ADB unter Windows einrichten
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