I have not used internal oscillator for usb, though as grombeestje pointed out, clock trimming is likely important. I am interested how that works out.
What kind of device does it enumerate as, and what kind of data rate?
I have used many 072 and 042 parts as usb hid devices, though with an 8meg xtal. Never a glitch on the streaming data -- well, until the test house clamped a sleeve around the cable for hv pulse immunity testing -- it didn't like that
Layout could affect it if you don't have a short-ish/straight-ish 90-ohm diff pair, smooth transitions to the series resistors... A tvs should be a must, and a common-mode choke is a decent addition. I had pll spurs to knock down and found that 47pF from each trace to ground fixed that without affecting data.