symantec system recovery 2013 - offsite backup problems

Hello,

We have a backup job for 2 different external drives. The regular backup is performed ok most of the times, but we have problems with the offsite copy:

We have 4 partitions to be backed up in our computer. 2 of them are backed up in this job, but the remaining 2 partitions haven't been backed up for the past 10 days. The regular backup works well for all the 4 partitions. Does anyone have an idea how to solve this problem ?

Thank you