oct() expects a string.  In your case, $vPermisos already holds the octal value (Perl parses a bare 0777 as an octal number)... so no need for oct() with mkdir().  Or if you use it, set $vPermisos = "0777"; (note the quotes).

(As you have it, you'd end up with 0511, as the implicit number-to-string conversion in oct() would produce the decimal number 511 represented as the string "511", which oct() then obediently converts to the octal 0511 ...)