I haven't run into this specific issue, but method of specifying template files and syntax slightly changed between 6 and 7, so you might investigate http://drupal.org/update/themes/6/7#template_files_double_hyphen

On Sat, Feb 5, 2011 at 8:35 AM, Balazs Dianiska <csillagasz@gmail.com> wrote:
Hi,

I have tried to use the old Drupal 6 approach to theme views output,
such as rows and fields, that is creating the suggested template file
in my theme and adding the appropriate THEME_preprocess function to
template.php. In Drupal 7 this doesn't seem to work. Although my
template file is picked up, I can't use these preprocesses. Could
someone help me out and explain how this should be done, or point me
to the documentation on this? I have tried using hook_theme to
register my preprocesses, but to no avail.

Balazs