How to retrieve an external reference ?

To list the external references:

1. In the FeatureManager design tree, right-click the feature, component, body, or part and select List External Refs.

This operation is only available for items that have external references.

2. View information and set options in the External References For dialog box as described below.
3. Click OK.

Also check these links:

http://help.solidworks.com/2011/English/solidworks/sldworks/legacyhelp/sldworks/assembly2/external_references.htm

http://help.solidworks.com/2011/English/solidworks/sldworks/legacyhelp/sldworks/assembly2/HIDD_LIST_EXTREFS.htm

Philippe,

Since it is a sketch, you can open the sketch, pick Display/Delete Relations and then pick External  under the down arrow. If you are very lucky, you can Delete All and move your sketch.

Jerry Steiger