AddAttribute Operation gives an error.

[Sitraman Wills1]

Hi,
Due to the below error, I am now unclear on the semantics of the addAttribute operation. Should I be able to add any attribute name I want to a managed object identified by the uniqueID. Also the command works only if I comment out the unique batch item id ( if I include that I get a http response code 500....) any help much appreciated.
On using
<batches>
<batch>
<operation>Add Attribute</operation>

<attributes>
<attribute>
<name>Unique Identifier</name>
<value>SymmetricKey6-000000000000000000000</value>
</attribute>
<attribute>
<name>x-attribute3</name>
<value>Value2</value>
</attribute>
</attributes>
</batch>
</batches>
For the addAttribute operation, I get the following error....

java.lang.ClassNotFoundException: ch.ntb.inf.kmip.operationparameters.Xattribute3
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at ch.ntb.inf.kmip.client.gui.Test.createAttributeInstanc