You haven't given us enough information. It depends on where your gaps are and what is connected to what.
Here's a great resource for all things to do with DCC wiring: http://www.wiringfordcc.com/track.htm
Go to the section on wiring referse loops -- there are some diagrams that may help (this is one of those things where a picture or diagram really is worth a thousand words!).
If you still have questions, post some details -- a diagram would be best!
Your crossover track should be wired as one section with both rails insulated at each end. Tony's instructions say that the reversing loop should be longer than the longest train you are going to run through it, especially if you have lighted passenger cars or a lit caboose.
Do you have your reversing loop wired that way? From your description, it sounds like you have broken your reversing loop into two sections and one is not receiving any power.
He also advises that the insulated rail joints be staggered approximately 1/8 to 1/4 inch in some cases, if you're talking about the NCE PS-Rev module.
I have a basic oval track with a setion of track running through the oval making it a reversing loop. I am using NCE Power Cab and Tony's reversing unit. My engine runs through with no problems at one area of the reversing loop section but when it gets to the other section of insulated track it stops. Any ideas? I would think if it was wired incorrectly it wouldn't work at all. Thanks.