I just upgraded to 10.1 SP1 a few days ago and am having label issues with an mxd that originated in 10.0. In 10.0, I had setup the mxd to use to use 14 different labelling classes for a street centerline feature class. I could go from page to page in DDP and not have any problems and exporting all pages was a breeze. Now when my DDP comes to a page that encounters one of these labelling classes (or a mix), it crashes. Label queries and all Maplex settings were unchanged when going from 10.0 to 10.1. I have tried Repair Geometry and exported the street centerline to a shp but that didn't work.
When I put the dataset into a new mxd I noticed that the labels showed up and didn't crash right away. However, that was because I had change the Label Engine from Standard to Maplex. Then I had to set the Placement Properties for Maplex - here are the settings as they were in 10.0:
-Street Placement -Position: Center Curved -Stack Label off -Overrun feature on - 16 pts -Remove duplicates on - 7 inches -Feature weight 750
I noticed there is a new option under Label Density called Connect Features, which is checked, but it is disabled. I'm not sure if this affects anything.
Mxds can become corrupt for a number of reasons, but this is often fixed using Save As to save the document under a different name. If you have done this and are still experiencing crashes, we'd like to take a look at it. Please submit a support request to your local distributor or to ESRI Support Services, and an analyst such as myself will be happy to investigate the issue with you. http://support.esri.com/en/
The line connection option was available at 10.0, but it was a global parameter that applied to all label classes in the map. Now you can choose a different connection method for each label class. It is grayed out when the street feature type is selected because street labeling has its own special connection rules.