Gittin 80 - Errors in Get
If one made any deviation from the rules of a Get, such as, being in Babylon, dated it according to the calendar of Rome or Greece, or even dated it from the construction or destruction of the Temple, or incorrectly named the city of writing, the Get is invalid.
According to Rabbi Meir, the woman needs to leave her new husband if she re-married, but can not return to her previous husband. She also looses her Ketubah payment from both, and many other benefits.
However, prevailing ruling is that she does need another Get but is not penalized as above.