Official Description
6.6.5.2 For write, it is an error if the value possessed by the expression is not assignment-compatible with the buffer-variable.
Simplified Description
In other words, it is an error to write a value to a file, if the value is not assignment compatible with the file type's component type. Or to put it another way, it is an error to write a value to a file, if the value is not a valid value for that file. For example given:
type
positive = 0..maxint;
var
f : file of positive;then
write(f, -1);is an error since -1 is not assignment compatible with 0..maxint.
Error Handling
This error is reported if range checking is enabled.