David,
I digged a little bit following your hint into Eclipse.

menu Windows / Prefernces (by user !) presented this image  

and this is the content of storage_location 

I doubt that without hijacking your (Windows ?) account this can NOT be misused.
 

Alex,
add Parameter  

Parameter XMLTYPE = "A_CHILD";

to one of your child classes
inherited comment is somewhat vague:

/// This parameter provides the default XMLTYPE for the class. If it is
/// empty then the class name will be used to construct a default XML type.
/// 
/// The default XMLTYPE is used when naming and referencing this type
/// in a schema and the schema context did not provide an XML type name.

documentation  is more precise:

For an XML-enabled class or a property that is based on an XML-enabled class, the XML type is determined as follows:
If the class has a value for the XMLTYPE parameter, that is used as the type name.
Otherwise, the short class name is taken as the XML type name.

so you would have 2 different classes with the same type:  CHILD
that's not allowed in an XML schema they have to be unique.

This is not Eclipse. What's your expectation?
JAVA is not a language used in Caché

class %SQL.Statement has a special property named %SchemaPath for this case.

property %SchemaPath as %String(MAXLEN="");

%SchemaPath provides a list of schema names for resolving unqualified names during statement preparation. By default, its value is null; to set its value, use a comma-delimited list of schema names

I personally deeply distrust all products from Microsoft and their management tools

BUT:

If your Caché is installed on a 64bit Windows you also need to use 64bit ODBC drivers.
Removing the 32bit DSN for Caché might solve your issue.
As your screenshot says (in German) you can do this only with a 32bit ODBC administrator tool. 
 

the only thing which i have done was installing some windows update

This was enough to confuse Eclipse.
Run Updates for Glassfish and/ or Eclipse inside Eclipse and the setup is updated.