ip route cache failed to work with 802 ISDN modem?

[penghon]

once I enable ip route cache in my ISDN 4 port BRI U interface on my 7206 with MPLS, the ISDN line would fail.

Are there any reason why should the route caching fail?

[tepatel]

Need to kow more about symptoms of failure like

1)Does isdn line connect fine at isdn layer and PPP layer?

2)Does Routing after connection fails?

3)ios version and config on 7200

etc..