You define the variable beta on top of the code, but this does not mean, that it is known in all subfunctions. Pr, gamma and lam are not known inside also.
Either define the constants, where they are needed, or provide them using an anonymous function:
sol = bvpinit(linspace(0,5,50),[0 0 0 0 0 0 0]);
fcn = @(t,y) bvpexam1(t, y, beta, gamma, lam, Pr);
sol1 = bvp4c(fcn, @bcexam1,sol);
function ysol = bvpexam1(t, y, beta, gamma, lam, Pr)