SPException: Field type is not installed properly

During my trial to create a custom cascade filtering lookup field, I run into the following exception:

SPException: Field type is not installed properly

There are several possible situations that can cause this error. E.g. using the optional field SPQuery in the fldtype_.xml is not allowed for custom field (see also http://msdn.microsoft.com/en-us/library/aa544201.aspx).
However, this was not my issue. I made a little (stupid?) mistake in the xml file. The field FieldTypeClass should show the full class name (including the entire namespace) as well as the full assembly name (I forgot the class-part, as shown in bold). So it should look like this:
<Field Name="FieldTypeClass">Dnm.SP2010.CF.AutoFilteredLookup.AutoFilteredLookupField, Dnm.SP2010.CF.AutoFilteredLookup, Version=1.0.0.0, Culture=neutral, PublicKeyToken=93ec60d3306981cd</Field>