Error: Failed to get the ItemType with ID undefined.

Hi, I have got a repository which I am trying to make use of. When I try to create items for a particular Item Type, I face a problem. Whenever I select the navigation item from the TOC category and try to create an item, I get the error message "Failed to get the ItemType with ID undefined." But I could verify that the Item Type exists. I have copied the whole error text below. Do any of you why this problem occurs and how it can be resolved? Error message: Failed to get the ItemType with ID undefined. Error details: <SOAP-ENV:Envelope xmlns:SOAP-ENV="">schemas.xmlsoap.org/.../"><SOAP-ENV:Body><SOAP-ENV:Fault xmlns:af="">www.aras.com/.../faultcode><faultstring><![CDATA[Failed to get the ItemType with ID undefined.]]></faultstring><detail><af:legacy_detail><![CDATA[Failed to get the ItemType with ID undefined.]]></af:legacy_detail><af:exception message="Failed to get the ItemType with ID undefined." type="Aras.Server.Core.ItemTypeNotFoundException"/></detail></SOAP-ENV:Fault></SOAP-ENV:Body></SOAP-ENV:Envelope> Thanks in advance. Alexis.