Exceedingly Slow Speed - Copy Aperture Library to Time Capsule

Is it possible that the Combination of "Aperture Library" and "Time Capsule" make transfer slow (about 0.1MB per second or even less)?

The trouble I'm having is very strange
- very fast transfer (>10MB per second) moving large .avi files to Time Capsule
- very fast transfer (>10MB per second) moving Aperture Library to other Hard Disks other than the Time Capsule
- exceedingly slow speed (<0.1MB per seconds at times, but sometimes it's much faster like normal) when moving Aperture Library to Time Capsule

This is very strange and I even asked Apple Care to change another Time Capsule for me thinking that the Time Capsule is at fault but same problem recurs.

Please help and many thanks!!