Details

This message is generated when the indicated value of the FormatType option is not among the types listed in the value of $PrintForms.
Off[message] switches off the message; On[message] switches it on. For example: Off[FormatType::ftype].

Examples

The value of FormatType is not among the types listed in the value of $PrintForms:

Wolfram Language code: With[{s = OpenWrite["TEST", FormatType -> cform]}, Write[s, 0];Close[s]]

Wolfram Language code: $PrintForms

This shows a valid value for the FormatType option:

Wolfram Language code: With[{s = OpenWrite["TEST", FormatType -> CForm]}, Write[s, 0];Close[s]]

Remove the test file:

Wolfram Language code: DeleteFile["TEST"]

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