Strange error messages - Units-of-measure

Unhelpful/strange error message on incorrect option type icon placement.
#### Repro steps

`let f (on:option int) = Option.bind (fun n -> Some(n+1) ) on`
#### Expected behavior

An error message like `option type expects the format of option<'a> or 'a option`
#### Actual behavior

Generates the error `error FS0706: Units-of-measure cannot be used as prefix arguments to a type. Rewrite as postfix arguments in angle brackets.`

edit: fixed error in code (ty @cloudRoutine)