Real Player and Adobe Flash perform very similar/overlapping functions, at least for some things where you might use either of them.

If you're trying to install Flash, Adobe may tell you to disable Real Player. If you're trying to install Real Player, Real.com may tell you to disable Flash.

Neither provider will tell you what conflicts between the two make it inadvisable to have both enabled at the same time, although there do seem to be some "ego conflicts." As when the teacher says the kids "don't play well together" it's often because certain of the "mommies don't get along" so there may be some of that too.

Then, of course, there's the "third party" factor, since Microsoft doesn't really seem to like either very much - since they both(?) stopped letting Mickey put them in Windows as free/default options.

John