LSMW error in CRM 7.0

We're upgrading to CRM 7.0 and as part of the testing I moved out LSMW projects to 7.0 to test. I have a project that created Contact BPs that works fine in CRM 4.

In Maintain Object Attributes I have the following:

Message Type: CRMXIF_PARTNER_SAVE_M

Basic Type:CRMXIF_PARTNER_SAVE_M02

When i run LSMW to create a contact BP Idoc processing fails with error message:

Message no. CRMXIF_PARTNER001

External partner category/number / is not unique

I was not setting the External partner category/number field so i tried setting it using IDentification Type CRM001 and some numebr but I get the same error. I have checked BUT0ID and the ID is DEFINITELY unique

Any ideas greatly appreciated

Thanks