This error may come about when printing an invoice. It has to do with the changes that were made in the invoice template, which is affecting the population of the invoices.

The first step is to go to Setup>Firm Settings>Invoice Templates

Find your usual template and click edit.

**Note that currently, if you select All text and change the font, this can cause this error, as the font change effects the tables (we are working on a fix for this!) If this was the only change you made, we encourage you to close the template and click "Restore" to the right. this will remove that change and your template is good to go. 

If you did not change the font, the issue may be with one of the tables or fields. If you can restore the template, that is what we recommend. Otherwise, give support a call, and we can try to work with you to discover the issue.