Line 680, Column 274: Duplicate ID menu-item-39.

Line 680
<http://validator.w3.org/check?uri=http%3A%2F%2Fecoventi.co.uk%2F&charse
t=%28detect+automatically%29&doctype=Inline&ss=1&outline=1&group=0&No200
=1&verbose=1&user-agent=W3C_Validator%2F1.3+http%3A%2F%2Fvalidator.w3..or
g%2Fservices#line-680>, Column 274:Duplicate ID menu-item-39.
…post_type menu-item-object-page alpha"><a
href="http://ecoventi.co.uk/home/"><…

I am totally new to all this but have been able to fix 5 errors so far
but now im a bit lost plaese help me

www.ecoventi.co.uk