REBOL 3 Errors: expect-set

Two series values were used together in a way that was not compatible. For instance, when trying to do a union between a string and a block.

Message:

["Expected one of:" :arg1 "- not:" :arg2]

Example:

filter-error try [union [a b c] "a b c"]
** Script Error: Expected one of: block! - not: string!
** Where: union [a b c] "a b c"