Last week, Jennifer Aniston fired back at US Weekly in regards to a report that she was engaged to beau Vince Vaughn "with a ring bigger than Brad's"

"They are not engaged. The Us story is a complete fabrication," retorted Aniston's flack Stephen Huvane. "She has no ring, there was no proposal and they are not engaged. I could not be more clear about this," Huvane said.

Now Star has learned the shocking reason why the two have had some issues as of late; Jen has made it clear to Vince that she's more interested in in building her big screen career than having babies any time soon. "Vince, like Brad, wants to be with a woman who wants to build a family with him,' a source says. "You'd think Jen would have learned her lesson!" "Vince has been pushing for marriage from the get-go," says a source. "But this summer, they've had many disagreements over how they see their future." (source:bosh)