Hi Retrotel,
By removing the main filter, do you mean you removed the resultReportFilter action result? Did you also remove it from the Where Script in the Generate Report action settings? If you post the full error message here I might be able to give some insight.
However if the only filter you need is on the date field, you should be able to make this much simpler. Your filter will need start and end dates, and you could generate these dates automatically in some cases, like for "two weeks ago" using Date Add actions with negative values (http://www.methodintegration.com/method/kb.aspx?folder=methodcrm&article=Date-add&id=137). For example start date = current date-14 days, end date = current date-13 days.
The default Genrate Report action on the screen uses an advanced script to filter, which is much more powerful but more prone to errors if the where script isn't formatted properly. This may be the issue you are facing. Instead, you can use a Regular Script with 2 Where conditions, one where date > start date, the other where date < end date. If you wanted you filter by sales rep as well, you could add a 3rd where condition. For more information please see http://www.methodintegration.com/method/kb.aspx?folder=methodcrm&article=Generate-Report&id=151.
If you have any questions about this just let me know.
-Russell