This usually happens when the table prefix is manually changed but some changes have been overlooked.
Go to your user_meta table and have a look at the meta_key column. Check if fields like wp_capabilities have been changed to use the wp1_ prefix. Also look in your wp1_options table to check that user_roles has been changed to wp1_user_roles.
When the table prefix is manually changed, the prefixes on these fields in user_meta are often left unchanged:
capabilities
user_level
user_settings
user_settings_time
Check them all. You can quickly identify which ones haven’t been changed by running this SQL query:
SELECT * FROM `wp1_usermeta` WHERE `meta_key` LIKE '%wp_%'