If you are having problems uploading changes from the mobile device back through server and into SDE. I had this issue with ArcGIS Mobile for 10.0 build 2550, i have yet to have this issue with the 10.1 suite.
Try these steps:
1) Stop the mobile service through Catalog or AGS Manager
2) Removing the spatial index on the layer that is failing to upload in Catalog
3) Re-start the mobile service
4) Try the Post/Syncronization again; if it works, stop the service and re-create the spatial index in SDE if it doesn't work see next step.
5) Get Creative, there is an app that was created that can move the mobile cache to a series of shapefiles that you can use to append, delete and insert all of the data collected in the field.
Hope this helps,
Bryan
