Upgrade your server and client to Subversion 1.9.
If the out of date error randomly occurs when you run commit in cases when it normally should not, then it may indicate that you are using an outdated and unsupported Subversion 1.7 or older client or server.
You should upgrade the server and clients in order to solve the problem. See the relevant Subversion 1.9 Release Notes entry: "Out of date" errors when committing over HTTPv1.