To edit or add quick void reasons you want to go to your back office and then store settings. Then select order entry and in the bottom right you will see your Quick Reasons for voiding items or orders and you can add or edit these here. 

To change your sales tax you want to log into the back office and then go to your store settings and then click on the taxes tab. 

 

From this screen you can adjust a current tax rate.

A guest check shows the price of the check for the customer, and the receipt will show the payment has been taken. You can disable this by going into back office and then into the station settings and selecting the printer tab, after this make sure the receipt printer is selected and make sure there is not a check next to “Do not prompt user to print guest check when finished in order entry screen” then you will not be asked if you would like a guest check to print. 

Periodically (for example, every two weeks), use the Compact Database feature in the Back Office. Compacting the database shrinks it and re-claims its unused space. This makes the database smaller, faster, and more efficient. To compact the database, go to the computer that holds the database. Close all other client stations connected to this database computer. Navigate to the Back Office and click “Compact Database” to start the compaction process. Once finished, you are notified that the compact process has been completed successfully.

This error refers to database corruption. Perform a backup first then Try using the compact database feature. Another option is to use the jet compact utility (advanced users) usually performed by a technician.