This is a complicated problem caused by the fact that 6.26.1 did not cope correctly with changes in the way some species were set up in the dictionary. As long as dictionary upgrade 00000003X was run after upgrading to RC 6.27 or 6.28 it should now be OK. If the upgrade to 0000003X was run with 6.26.1 installed then 6.26.1 will have corrupted the dictionary by undoing the fix in 0000003X.
However, there could be something else going on here and I will need to make sure the problem in 6.26.1 has actually been resolved in 6.28 and that the dictionary upgrade to 00000040 hasn't caused another problem.
R6 is trying to stop users using taxa for data entry where they or their parents are considered redundant. This used to be determined by the R6 application, but after 6.26.1 is determined by entries in the dictionary, which allows more control. In some instances it could be that some previously used taxa have become redundant so R6 may be correct or we may have inconsistencies in the dictionary.
Please continue to let me know any problems you come across and which versions of R6/Dictionary you are on.
Mike Weideli