Did a cvs update about four hours ago and found the subject function
to throw an error on incorrect number of arguments.  Looks like it
happened in the most recent change to gnus-sum.el based on a cvs diff.
The interactive function was changed to allow for both include and
exclude by means of the prefix arg, but the resulting call tries to
set up three arguments, but gnus-summary-limit-to-author only has one.
The attached patch fixes the incorrect argument backtrace and I think
provides the intended previous behavior of / a including the ability
to exclude if current-prefix-arg.
-- 
Dave Goldberg
david.goldberg6@verizon.net