Can you check whether the changeset you're attempting to view does not have a log message that contains non-UTF8 characters? This is a typical cause of this kind of error.
SVN log messages should only contain UTF-8 characters.
0.9 series were more permissive about invalid characters, they were unable to detect this kind of issue. It does not mean a bug has been introduced in 0.10 series, but that the latter do not accept invalid characters anymore.
You can also search for "can't decode bytes" in the ticket database, as I'm confident several other tickets deal with the same issue.
BTW, you'd better upgrade to 0.10.3.1 as it fixes several functional and security issues.
