How to change settings to avoid duplication e.g postname| sitename

Hi there,

Thanks in advance for any help. My site – My Piggy is showing in webmaster tools that it has duplicate title tags e.g

Buzz Card | MyPiggyWiggy – is saying 2 errors for 2 pages:
/tag/buzz-card/
/tag/buzz-card

How do I make sure I only have one page? No idea how this has happened