Catherine Zeta-Jones has for the second time entered a treatment center for her bipolar disorder, TMZ reports. Zeta-Jones checked in yesterday and is doing a 30-day program; her rep tells Radar she's just being "proactive" and "is committed to periodic care in order to manage her health in an optimum manner." As another source puts it, "It's maintenance." Yet another source tells People there's no "big problem," Zeta-Jones just wants doctors to monitor her medication and chose to do it now because she's "between projects." She previously stayed at a mental health facility in 2011, when the disorder was first revealed.