You want to mount C:\ directly.
mount C C:\
By mounting C:\LOTUS as C: within DosBox, C:\ within DOSBox is the same as C:\LOTUS on the system itself. That is, If you have these folders on the PC you are running DOSBox On:
C:\LOTUS
C:\LOTUS\STORE
and then you mount C: as C:\LOTUS within DosBox, then Dosbox has the following directories:
C:\
C:\STORE
it does not have a C:\LOTUS or a C:\LOTUS\STORE directory. Thus the errors you are seeing.