This message is generated when the value of the Modulus option in Factor exceeds the largest value supported in this version of the Wolfram Language.
This message is not normally used in the current version of the Wolfram Language since other messages will be generated and the calculation will fail before this message is generated.
In most versions of the Wolfram Language, the largest supported value of the Modulus option is 46337, which is the largest prime number that is less than the square root of the largest machine integer on most computers.
Off[message] switches off the message; On[message] switches it on. For example: Off[Factor::priml].