I spent more than a hundred tests and is now convinced of the situation.
Floppy drive is not affect.
If you install DSS7.0up11 or DSS7.0up12 on a virtual machine with 2048M RAM, then DSS will not boot. If you then latter change the amount of RAM is also not boot. DSS7.0up5 not affected this issue.
If you install DSS with another quantity of RAM - that works.
Then it is possible to change to 2048M - all works fine.