I should add that I also tried removing the seo-booster directory using FTP and re-installing from the repository, but that did not solved the problem.
Hello tappenden_de
Thank you for your bug report, sorry I was away and not able to respond earlier.
I have just checked the plugin and verified I can download and install correctly. I am curious which PHP version you might be running or if there was a problem with the recent WordPress 4.9 release?
I have just pushed out a new version that includes a couple of fixes, could I perhaps ask you to try again if it works?
I tried updating to plug-in version 3.2.9 but it didn’t solve the problem.
The site was running PHP 5.3.29 and WordPress 4.9.1.
I notched the site up to PHP 5.4.45 and the plug-in now works!
Hello tappende_de
Great to hear that it was the PHP version that was the problem 🙂 Sorry for the trouble you went through.