CES function estimation
You should always validate statistically your model, running various model diagnostics. It appears you work with time series (single country?).

Here, certainly autocorrelation may be an issue. After all, your series for capital is by construction an autoregressive equation with a forcing factor (investment).  

Software packages usually warn for signs of multicollinearity.

Also, a serious issue could be that of endogeneity of regressors.