This message is generated when the argument in HermiteDecomposition or LatticeReduce is a matrix with at least one element that is neither an exact integer nor an exact rational number.
Off[message] switches off the message; On[message] switches it on. For example: Off[HermiteDecomposition::latm].
Examples
Basic Examples(1)
The element 4.5 is a real number rather than an exact integer or a rational number:
The inexact number can be converted to an exact rational number using Rationalize: