You are trying to find a zero of a function. This means Matlab will look for an x-value where the sign changes. During this proces it encountered a -inf value, after which it broke off its search.
What you need to do is written in the warning message: either check if your function is indeed the function you ment (i.e. check for typos), or adjust the starting value. If you have the function y=x and you start looking a x=100 and only increasing x, you'll never find the crossing. Apparently something equivalent has happened here.
Your Matlab is not broken, it just did not find the result it was looking for.