A warning about what?

Note also that your expression is equivalent to 2*cosh(.0057195*x)=1, which has no solution for real x. There is, of course, a solution for imaginary values of x, and maxima can solve 2*cosh(.0057195*x)=1.

And maxima 5.27 appears to be finding roots of the original equation, but I didn't wait. For .00571, maxima returns a long list, but they're not actually solutions because x appears on both the lhs and the rhs. That's a bug in solve.