WP_Error could not be converted to string

After logging in with Steam this is what I get:
Catchable fatal error: Object of class WP_Error could not be converted to string in /home/zenforic/public/center/wp-content/plugins/wp-steam-auth/inc/functions.php on line 14

To figure out what variable was breaking the code, I put each on a new line. The one that has it broken is $userId. For further investigation, I also enabled debug mode. That revealed these extra lines:

Notice: Undefined offset: 0 in /home/zenforic/public/center/wp-content/plugins/wp-steam-auth/wp-steam-auth.php on line 107

Notice: Undefined index: uptodate in /home/zenforic/public/center/wp-content/plugins/wp-steam-auth/inc/functions.php on line 32

The page I need help with: [log in to see the link]