xsd with import tags

Any clue as to why the following error is thrown while creating a schema using the XBRL xsd (http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd) on webMethods 7.1.2.
Note: I’ve downloaded all the dependent xsds into same folder locally.

errorMessage: [ISC.0082.9709] Type derivation not OK: attribute declaration to be restricted is not found in the base type definition

From 8.2 SP2 release notes, I’ve noticed a similar error, PIE-19218 (IS_8.2_SP1_Core_Fix1), but not sure whether it is the same issue I’m facing.

This is from the ErrorReference:

Cause: In a complex type derivation, an attribute declaration restricts the use of an attribute. However, this
attribute declaration is not found in the base type definition.
Response: Make sure that the attribute declaration is present in the base type definition.