Message 13043 - can't "Create and release demand"

My problem refers to SAP ME 5.2.3.2:

Trying to "Create and release demand" results to the error message:

"Not enough quantity is available to release shop order xyz (Message 13043)"

However all three (3) materials of the BOM have inventory much higher then required to fullfill the requested shop order.

Details of the BOM:

- Two (2) positions are purchased material, one (1) was manufactured.

- all three materials have "Qty Restrictions":="Any number" because they have liters or kg for "Units of Measure"

- at the BOM the "Assembly Quantity" therefore is "Any number" too, like 0.53, 1.3 ...

Thank's in advance for your assistance.

Bernhard