Fatal error: Class 'Diff' not found ....

hi

When I try to compare 2 entries
I get the following error

Fatal error: Class 'Diff' not found in /public_html/sites/all/modules/diff/diff.module on line 366

when i used 6.x-2.20

or

Fatal error: Class 'Diff' not found in /public_html/sites/all/modules/diff/diff.module on line 273

when i used 6.x-2.x-dev

i used
Revisioning 6.x-2.7