You might try deleting the scheduled task completely and adding it back by creating a NEW remote back up task. I'm not certain, but I know that MODIFY doesn't quite work properly at least with Network Shares tasks so I wonder if that's the same case with the remote back up task list. Have you modified the task at all? Also, try checking "Ignore Existing Files." Be careful with this option as I have had the target volume wiped clean without my consent by not checking it.
It is a slow process, but 20 MB shouldn't take that long. I remotely back up 4.88 GB of data on a daily basis, and I estimate it takes about 12+ hours on a DSL line with 50-60 KB/s upload speed.