Correct SNIR computation units
You'll have to convert back into linear units before you can evaluate the SINR formula.

${\textrm{SNR}_{linear}=10^{\big(\frac{\textrm{SNR}_{dB}}{10}\big)}}$ and likewise for CIR...

${\textrm{SINR}_{dB}  = 10 \log_{10}(\frac{1}{\frac{1}{\textrm{SNR}}+\frac{1}{CIR}}})$

${BER = \frac{1}{4{\textrm{SINR}}_{linear}}}$