Merge Drawings problem-"internal data structures too large"

We regularly use the 'duplicate' feature within an Intralink (3.4) workspace
to duplicate and rename drawing and any associated parts. Many assemblies
are very similar so this provides an easy start point for a design with some
of the work being done for free.

We also use the 'merge' drawings feature within Proe (2001) to merge two or
more drawings together.

We are increasingly getting an error message
'Cannot merge, internal data structures would be too large' when attempting
to merge drawings together and it seems related to the drawings we have
previously duplicated.

Has anybody else had this issue and if so, how did you manage to resolve it.
Is there any way to cleanse or purge a drawing of any excess 'baggage'?

Hope this all makes sense,

Anthony