Can a creature have in operation at the same time both the 6th-level Sor/Wiz spell contingency [evoc] (Player's Handbook 213) and the 6th-level psion/wilder power psionic contingency [clairsentience] (Expanded Psionics Handbook 86) ?
As written, Psionic contingency specifically says that only a second casting of another spell named 'Psionic contingency' dismisses the first casting, and vis versa for Normal contingency. Making no mention to it's counter part, or mentioning similar effects.
As such as neither would dispel one another, barring any Magic vs Psionic transparency your DM my apply.
The old official 3.X errata archives did not create any additional foot notes regarding the issue either.
While not a direct answer to your question, if you are looking to stack contingency effects may I direct you to the feat 'Craft Contingent Spell' (Complete Arcane, P.77 / P.139 & Unapproachable East, P.42 / P.46) which specifically lays out that a creature may bear a number of Contingented Spells equal it's HD. These effects are treated as unslotted magical items. Which on top of allowing one to use mutliply triggered effects, also allows them to stack with the spell (or psionic) version of contingency.
A strict reading of the text would suggest yes. Psionic contingency isn't one of the "as the X spell, except..." powers, it has an explicit description which says you can only have one instance of psionic contingency active at a time.
That said, if magic-psionics transparency is in use, I might well rule at my table that they conflict under a "same effect, different source" argument.