When configuring ISIS over NBMA networks (such as ATM or FR) don’t forget that you probably configured static mapping such as

For ATM

interface ATM 0/0
 pvc 0/109
  protocol ip 1.1.1.1 broadcast

For FR

interface Serial 1/0
 encapsulation frame-relay
 frame-relay map ip 1.1.1.1 109 broadcast

but you know that ISIS uses CLNS as a protocol and not IP so you won’t get adjacency there.

To correct this, you need to map CLNS also

interface ATM 0/0
 pvc 0/109
  protocol clns 00 broadcast

For FR

interface Serial 1/0
 encapsulation frame-relay
 frame-relay map clns 109 broadcast