For Cross database version you should use Export/Import Not datadump , You can import your 11g expdp dump file into Oracle 10g if you make sure you use "VERSION=10.2" parameter during export.
Check Does impdp support 11g to 10g import?
Edited by: Osama_mustafa on Oct 24, 2012 8:03 PM
Pl identify exact "11g" and "10g" database versions, along with OS versions. The documented VERSION parameter of expdp may be applicable