Please try this:

1) Quit SlingPlayer. 
2) Move (so you can easily restore them as needed) all com.sling* 
files out of

~/Library/Preferences/ 
~/Library/Preferences/ByHost/ 
~/Library/Application Support/Sling* 
/Library/Preferences/ 
/Library/Preferences/ByHost/

(you may not find settings of SlingPlayer in all of these, but these 
are the places to look for them) 
(this should reset your settings - unless Sling does something special 
with setup)

3) Start and set upSlingPlayer. 
4) Press P and U where Play and Pause make sense.

Best regards, 
Felix