If invoice is not generating and just gets stuck when you try to create,It may be your data issue,you can follow given steps:
Step 1:First you need to close your BUSY forcefully,
Step 2:Then open the BUSY and click on Backup Data,take latest backup of your company on your system.
Step 3:Then Click on Reindex DataBases,select that company which you are facing in issue,then run this process,
Step 4:After reindex successfully,re open the company and enter a voucher again and check, it will be resolve.
Step 5:If it is still showing issue then check your data size of company,
Step 6:If the Data size is heavy as above 2GB and you are using access,so we are recommend, you need to convert you BUSY
access to sql version,
Step 7:Set BUSY as compatible mode,right click on BUSY icon,click properties,then click compatibility,check the check box Run as administrator.