When I tried to create the custom field it said I had reached the limit and couldn't create any more. I deleted an existing custom field and tried to create the custom field I need but it still says I've reached my limit.

How many custom field am I allowed and why won't it just let me delete on and create a new one?

This is starting to restrict my ability to produce targeted campaigns as I have a wide range of variable that I need to be able to include in a segment.