Please help Have got the 'This library is being used by someone else. Try opening it again later' message

SO SO SO frustrating. Endnote 8 was working just fine then all of a sudden it freezes and whe I restarted my Mac it keeps giving me this message. Have restarted several times now and ended up uninstalling and reinstally…but this time endnote 9. However it’s still giving me the same TEDIOUS and FRUSTRATING message. What the hell is going on and how do I fix this??? Really is Endnote worth this waste of time when I have an assignment due??? Way to make people lok for a better service elsewhere. Please if you can offer suggestions (keeping in mind I am not a computer expert) it would be much appreciated