Cross-Class

ok, being a level 19 Full-Blown ranger.. i find it quite hard to solo, heres my question

is there any advantage to being a single class.. if so why are there so many cross-classed people?

There are no advantages to single-class and you shouldn't solo: GW is a team-game.

yep
indeed it is bad to have just 1 class

There is absolutely NO advantage to not having two classes other than having less skills to choose from, if you consider that being an advantage. That may make it easier to manage, but most people would consider that a disadvantage. If you are having trouble staying alive, perhaps you should pick monk as a second class.

EDIT:
Having a second class will not make you any less of a ranger in ANY way. You can still choose to fill all of your skill slots with ranger skills if you choose to. If you are grouping with 3 monks and monk is your second class, you can choose to fill all 8 slots with ranger skills and be just as good of a ranger as you were before you chose a second class.