Two backups at the same time causing VSS errors

Hi

We have an MSL 4048 with 2x LTO 5 tapes

,if i set two jobs to run simultaneously 

One starts at 9:00 PM and will end around 10:00PM and the other starts at 9:30PM and will end around 10:30PM

The jobs will finish with this exception:

V-79-10000-11233 - VSS Snapshot error. A Microsoft Volume Shadow Copy Service (VSS) snapshot is already running on the target computer. Only one snapshot can run at a time.  Try running the job later.

Does it mean that becuase VSS was used in the first job, it cannot run twice?

Does it means that as a concept, even that the auto loader got 2 x LTO drives, it is better not to run two jobs at the same time?

Thanks