why do I get this problem 'Attempt to execute SCRIPT integral as a function:'?

I integrate a function by using 'integral' command, and showing the problem as'Attempt to execute SCRIPT integral as a function:', How can I resolve it?

This is my function

'P_{Out}^{{\mathop{\rm Sec}\nolimits} } = 1 - {\left[ {\frac{1}{{{\Omega {RU1}}}}\int\limits{{T_1}}^\infty {\left\{ {\exp \left( {\frac{{ - \left( {\Delta - 1} \right)}}{{w\left( z \right){\Omega {U2R}}}} - \frac{z}{{{\Omega _{RU1}}}}} \right)} \right\}} dz} \right]^2}', where, '$z = {\left| {{h{RU1}}} \right|^2}$, $\Delta = {2^{2{R_{TH}}}}$, $w\left( z \right) = \left( {1 - \beta } \right)\left\{ {\frac{{\eta \beta {\rm{ }}Pz}}{{\eta \beta {\rm{ z }}{N_0} + {N_0}\left( {1 - \beta } \right)}} - \frac{{\Delta P}}{{\left( {1 - \beta } \right)Pz + {N_0}}}} \right\}$ \\ and ${T_1} = \frac{{\left( {\frac{{\Delta - 1}}{{1 - \beta }}} \right) + \sqrt {{{\left( {\frac{{\Delta - 1}}{{1 - \beta }}} \right)}^2} + \frac{{4\Delta P}}{{{N_0}\eta \beta }}} }}{{2\left( {\frac{P}{{{N_0}}}} \right)}}.$'