You can find that some hubs are slightly different in size - and the width of the axle parts can make a difference
Some times forks can be tight - but if you can prise apart the forks a bit, you should be able to get the hubs in there
Or you could find some slimmer axle washers and then the forks might work better
if you still have trouble - post some pic's and we can go from there
hope this helps - cheers B