Very high 260/230 absorbance ratio of an RNA sample
Gergana is right about the effects of the Guanidine isothiocyanate, but not the details there of.  Guanidine isothiocyanate absorbs strongly at 260 and NOT 230 (guanidine hcl is the one that absorbs strongly at 230).  As such if your RNA is highly contaminated with guanidine isothiocyanate, which is used in at least one buffer in just about every RNA prep kit, your 260/230 is going to be much larger then 2 (also the "concentration" will be artificially high.  So if you are getting a 260/230 of 25 and have a "concentration" of "1000 ng/µL" you may actually have less then 200 ng/µL of RNA and a ton of Guanidine isothiocyanate throwing everything off.)