Hello,
If you see this, it is probably because you have edited the invoice template using the HTML edition mode, which is highly not recommended (as it is said in the template manager).

To solve this, please edit the invoice template with plain text and fill the template fields with the original ones that you can find here:
http://www.joomlathat.com/documentation/invoice-manager/bootsrap-invoice-template
When you save it, you will have the default invoice template working. For further modifications, please use the plain text editor and not the HTML editor.

Another solution is to reinstall the component again and the tempalte will be be created again. Note that by reinstalling the component you won't loose your data because it is stored in the database and the reinstall process will not affect to it.

If you have any questions, ask us again