Open the Sales menu and select the Invoice List view. Under the Views panel, locate the Unposted Invoices list.
Record the invoice numbers of all unposted invoices for the period you are trying to post to QuickBooks.
Return to the Post to QuickBooks screen under the File menu and post each invoice individually - not by period. Continue posting invoices individually until the error appears. This will tell you which invoice has an illegal characters in it.
Open that invoice in the Sales Invoicing screen in ESC and review each line item. If any line item contains text that was copied from outside of ESC and pasted into the invoice, you'll need to remove that text and retype the information manually. This is to remove any hidden formatting or characters that may have been copied and pasted into ESC that may not be visible. Otherwise, look for unique characters or symbols that may have been used in the Description of an item (something other than standard punctuation marks).
Once the invoice has been corrected, resave the invoice.
Return to the Post to QuickBooks screen under the File menu and post that invoice to QuickBooks. That invoice should now post without any errors or disruptions. You may now post other invoices to QuickBooks as you normally would. If the error occurs again, repeat this process until every invoice has been correct.
To fix this issue the illegal characters must be removed from the XML stream. To do this, complete the following instructions on the computer that tried to post invoices to QuickBooks.
Open the Start menu or Start screen in Windows and type in %APPDATA% and then hit Enter.
When the Application Data folder appears on the screen, open the ESC folder from the list.
Delete the QBXML.log file from the contents of this folder.
Try to post to QuickBooks again. It should create the same error. Click OK to close.
If connecting to QuickBooks through the ESC Accounting Server, the ESC Client will hang. Use task manager to end the program and then restart it.
The QBXML.log file would have regenerated in the Application Data\ESC directory upon attempting to post. Open the QBXML.log file and view the last entry. It will show the transaction that caused the error.
Open that record in ESC and search for illegal characters. Remove them and resave the record.
Try the post again.
Repeat steps 1 - 6 if additional errors appear. Do this until the post works properly.