As addressed in the how to generate dues article, the system checks to make sure everything looks correct before allowing you to proceed with generating dues. In order for this check to be helpful, you need to know what to look for when you get the errors and what steps to take. This article should assist you with the most common troubleshooting tasks in the Generate Dues Wizard.
Review the Validation Screen for Failed Items.

The Failed Items in blue are actually a link you can click to review records that may be a problem.
Click the Failed Link and Open the report.txt file.

The file you open will give you the names of all the records that are failing to meet the wizard criteria. You may have to open a few of these records to determine what needs to be updated on the record or how you may need to adjust the query.
Troubleshooting a Query Error
Most of the validations are checking to see if people fit in the queries as expected. The Master Query should include everyone that will be billed in the dues cycle. The Schedule Queries should divide these people into groups for specific billing purposes. No one should fit into more than one schedule query. However, everyone in the schedule queries should fit under the master query. Think about it like a school. The Master Query is everyone who should be in the school and the Schedule Query is which classroom the person is assigned to. You can't be in a classroom without being in the school, and you can't be in more than one classroom at the same time. You also can't be without a classroom, so if you are in the master query, you must have a schedule query.
If there are a lot of people on the report.txt file
Check the queries. If you have a lot of people chances are you left a member type out of one of the queries or you forgot to create a schedule.
If there just a few names, check the membership records for missing or incorrect information.
It could be that you are missing data on a field that the schedule query is looking for but the master query is not so the person fits in the master but not a schedule query.
Your schedule queries may be missing criteria on the schedule so they have people that fit in both. You can add more detailed criteria to narrow the groups further.
Your master query may be too specific so someone is eligible for a schedule query but not the master.
*Note we see this most frequently in people accidentally using Status in one query and Status Reason in another which can cause issues with who fits.
Verify a Default Dues Option Exists
This is a pretty quick item to check. Every Dues schedule must have a Default Dues Option, so if you have only one make sure that is set to Yes. If you have more than one decide which one should be the one that members get unless they choose something else.
Verify that the Dues Option has a Required Product.
We almost never see this error as you usually are charging dues and requiring payment, but in some cases you may have people that you only want to charge an optional product for. The system requires you to have a required product, even if it is for $0.00.