Problems merging two branches - Subversion 1.3

Hi all,

We are facing some problems during a merge process from a branch to trunk (2
URL merge). Note that we didn't synch the branch with the trunk at any time.

We want apply all changes made in that branch back to the trunk but for some
reason the results that are we getting are very odd. Lots of files are not
merged nor added and for some strange reason all conflicts are tree
conflicts.

The command we are using is something like this: svn merge
branch_at_HEADtrunk@HEADWorkingCopyWhereTrunkWasCheckedOut

We know that the --reintegrate option is only available since version 1.5
and perhaps it's the right thing to do, but we cannot upgrade subversion,
it's out of our scope and impossible to accomplish.

May you help us please? Any help would be much appreciated.

Thanks in advance.

-- 
-----
Jonatan Soto