[Flow] Error "... name is already in use ..."

[Tomas M]

Hi members!

I'm new in this forum and here ist my first question about Flow.

I've defined a class with several protected properties each with some
validation annotations and ORM mappings.

Therefor I use

use TYPO3\Flow\Annotations as Flow;
use Doctrine\ORM\Mapping as ORM;

This works fine.

In a second step I've defined a new class which extends the first class with only
one more property. If I want to use there the annotation and import it like above,
i get i.e. an error like

"Cannot use Doctrine\ORM\Mapping as ORM because the name is already in use in..."

If don't use the "use" I get a message like

" [Semantical Error] The annotation "@ORM\ManyToOne" in property".

What is wrong with this?
Does someone haven an idea?

Thanks!
Tomas