Per the Congressional Budget Office: "enacting the bill would increase budget deficits from changes in direct spending and revenues by $7.2 billion over the 2013-2023 period."
The Democrats bill sought to replace $85 billion in cuts with cuts to agriculture and defense spending, and by opposing an effective minimum tax on people making more than $5 million a year -- a version of the so-called Buffett Rule.
Democrats wrote and intended the bill to be deficit neutral or better, but per a Democratic leadership aide, when CBO and the Joint Committee on Taxation scored the bill they concluded it didn't quite hit that benchmark. Democrats could in theory fix that by lowering the income threshold on the Buffett Rule or increasing the spending cuts or paying down less of the sequester or any number of tweaks. But that would require rewriting, re-scoring and refiling the bill, which is set for a vote today.
Republicans were going to filibuster this thing anyhow, so it amounts to a small messaging problem. But if you hear Republicans claiming their opposition was rooted in the bill's CBO score, now you know what they're talking about.