Remove Multisite not possible

Dear all,

i installed multisite and would like to remove it (there was someting wrong with it, i never created any site). I changed all the modifications i made in wp-config.php and .htaccess, I even went back to an complete older backup.

But: When i try to install multisite again i got a warning: an existing network was found. Please clear the database.
I can´t install a new network.

In permalinks there was a strange entry. I set them back to default.

Thanks for your help!