There is a bug in 0.7.5 in
roundup/backends/rdbms_common.py. On the line 1119 you
ask whether a value is instance of Date, if so, you
pass the value to the constructor of Date, which can't
do anything with it an raises an Exception. 

  File
"/usr/lib/python2.3/site-packages/roundup/cgi/templating.py",
line 868, in history
    d = date.Date(args[k]).local(timezone)
  File
"/usr/lib/python2.3/site-packages/roundup/date.py",
line 135, in __init__
    raise ValueError, 'Unknown spec %r'%spec
ValueError: Unknown spec <Date 2004-06-12.15:00:0.000000>

The real bug sits in roundup/date.py. There is a check
(line no. 125) for `tuple` attribute, which should be
`get_tuple` (or even better, isinstance(spec, Date).

I attach a patches for this bug.