Using the Action > Assign Review Rules option in GIFTS 6.4 causes an error. Please do not use this option as it is non-functional and was not intended to be included in GIFTS 6.4.
Also, within the Administrator Module, if you go to Setup > Reviewers > Review Assignment Rules and create a New rule or edit an existing rule, there is a related option called Apply Rule to GIFTS/MyGIFTS. This box is checked by default. If it is checked, and you use the Action > Apply Review Rules option in GIFTS, the error will occur. If it is unchecked, and you use the Action > Apply Review Rules option in GIFTS, you will be prompted with a message saying "No Review Rules are available to be applied to the selected Requests."
NOTE: In step 3 of creating a Review Rule in the Administrator Module, there is a visible Committee button. Clicking this button will also cause an error. Click OK to close the error message prompt.