Typically, OMP (like our other applications) uses URLs that look like...
...where everything up to (and including) the "index.php" part locates where the installation is on your server. After that, everything ("additional/parameters/here" in the example URL) identifies what part of the system you're viewing, and that part is parsed and handled by OMP internally.
The problem is that some servers are misconfigured in a way that results in these URLs not working. The disable_path_info mode uses an alternate way to generate URLs, but they're verbose and fairly ugly by comparison.
It might be as simple as changing an Apache configuration directive, but it may be more complex, and a large shared host may not be willing to do that. I'll take a quick look at the disable_path_info option in OMP, and if it's quick to fix, I'll post a patch on the above URL -- but if it's more involved I may not be able to prioritize it just yet.
Public Knowledge Project Team