You need to go to administrator menu "Extensions -> Modifications" and remove an old modification record (file). More info >
Please go to administrator menu "System > Settings > Default Store > Edit > FTP tab" and check your FTP credentials. Most likely you entered the wrong FTP Host. More info >
You need to check the FTP Root option in your FTP credentials (go to administrator menu "System > Settings > Default Store > Edit > FTP tab") . If this option is incorrect the extension was installed to the wrong directory. More info >
You need to try to re-install the extension. Go to admin 'Extensions > Modules' find the extension and click Uninstall button then install it again (click Install button). If it doesn't solve the problem, most likely your database user doesn't have permission to create a new table in the database. You can create the extension table manually from '.sql' file in the '.zip' archive with the extension or get permission to create a table from your hosting provider or website administrator and re-install the extension.
You need to try to upload the extension files again and re-install the extension. If it doesn't solve the problem, try to use another installation type (Extension Installer, VQMod, Marketplace).