I lifted this from the article linked to above....
There would appear to be three possible explanations for the lack of a time dilation effect in quasar light curves, all of which conflict with broad consensus in the astronomical community. First, time dilation might not in fact be a property of the universe, which would effectively mean that the universe was not expanding. Apart from the overwhelming support for the big bang theory, the direct measurements of time dilation quoted above strongly argue against this. The second possibility is that quasars are not at cosmological distances. This is an argument that was hotly disputed in the 1970s, with an emerging consensus favoring cosmological distances. This has subsequently been strongly confirmed by studies of quasar host galaxies at high redshift. The third possibility is that the observed variations are not intrinsic to the quasars but caused by some intervening process at lower redshift, such as gravitational microlensing. Although this idea has been strongly argued (Hawkins 1996), there is an opposing view that variations in quasars are dominated by instabilities in the central accretion disk. The reality of this mode of variability in active galactic nuclei is supported by detailed observations of Seyfert galaxies (Peterson et al. 1999) and gravitationally lensed quasars (Kundi et al. 1997), where the presence of intrinsic variations cannot be in doubt. The debate centers on whether this mechanism is responsible for the long-timescale large-amplitude variations that dominate the power spectra discussed in this Letter.
I like the first possibility
alex