Latex align error
===

Why does the following code give me an "Extra } or forgotten \right)" error? I have been through it and cannot work out why.

\begin{align}
C(t,xxx,\tau,N,X)&=N\Phi\sum_{i=1}^{n}\left[-(1+X_{\tau_{i}})P(t,T_{i})\left(\frac{\ln\frac{P(t,T_{i-1})}{(1+X_{\tau_{i}}P(t,T_{i})}}{\Sigma(t,T_{i-1},T_{i})}-\frac{1}{2}\Sigma(t,T_{i-1},T_{i})\right)\\
&+P(t,T_{i-1})[\left(\frac{\ln\frac{P(t,T_{i-1})}{(1+X_{\tau_{i}})P(t,T_{i})}}{\Sigma(t,T_{i-1},T_{i})}-\frac{1}{2}\Sigma(t,T_{i-1},T_{i})\right)\right]
\end{align}