I am trying to migrate the user accounts from one sandbox, to the next.

There are several custom feilds in the  user object, one of which has external ID turned on.

I can extract the users just fine. Except when I am upserting them, no record gets inserted:

ERROR com.salesforce.dataloader.client.PartnerClient - Errors were found on item ## 

ERROR com.salesforce.dataloader.client.PartnerClient - Error message:OC_User_ID__c not specified

This occurs for EVERY record, and non are inserted. Details about this custom field

Field Label: OC User ID

Field Name: OC_User_ID

Required: False

Unique: False

External ID: True

Default Value: [blank]

Length: 20

 As for the config file, The relevent stuff here:

<entry key="sfdc.entity" value="User"/>

<entry key="sfdc.externalIdField" value="OC_User_ID__c"/>

<entry key="process.operation" value="upsert"/>

<entry key="process.outputError" value="c:\dataloader\errorUpsertUsers.csv"/>

<entry key="process.outputSuccess" value="c:\dataloader\successUpsertUsers.csv"/>

<entry key="dataAccess.name" value="c:\dataloader\ExtractUsers.csv" />

<entry key="process.initialLastRunDate" value="2007-06-06T00:00:00.000-0800"/>

Inside ExtractUsers, the data is all there, The records all have an OC_User_ID__c entry.

Can somebody shed some light on this? Thanks