First: formats. What format have the mes field? Is it a text or a number?
Second: number of selections. How many selections are you doing using the field mes? If you select more than one value, it will be comma separated but not enclosed by single quotes, as required to a list of literal values. If you only select one value, again you need to use single quotes if the value is a text.
Third: Is the format of values in field "mesagenci" exactly the same as in field "mes"? If yes, are the both numeric? The "$(#MESOB)" will return a number (that's why you are using the "#" symbol in the dollar expansion) that might not match the format for the field "mesagenci".
I'd suggest you to use a slider object instead with all possible values for "mes" populating the variable "MESOB".
Hope that helps.