My use case is following:
I attach database A right from CD.
Then I remove disk with A from CD-drive and try to backup database B
Expressmaint returns following error in log:
Starting backup on 06.03.2008 12:06:48
Unable to open the physical file "F:\database_2007_Data.MDF". Operating system error 21: "21(....)".
Expressmaint finished unsuccessfully at 06.03.2008 12:06:48 with Return Code(-4)
So, can your tool backup specific database not checking other db's?