cryptic insertion means that in banding cytogenetics the insertion cannot be detected; when doing mol. cytogenetics suddenly a previously unexprected insertion event becomes obvious. Even with the knowledge that there is the insertion rechecking banding cytogenetic result you cannot even suggest it is there.

Cryptic insertion means that it's non detectable to chromosomic level but may be detectable by molecular techniques.

As others stated before, the word "cryptic" in fornt of any chromosome reorganization means that it is not detectable by classical cytogenetics methods such as G-banding and therefore requires Molecular Cytogenetics methods (Fluorescence in situ Hybridization) in order to detect such invalances.