Email variables block the sending

Hi, I’m using the IP and found some bugs on invoice e-mail sending. When I use the variables to format the message, making a template or not, the sending returns me an error (sometimes, the red gear, sometimes an error report with functions failing). Also, when I try to use two or more e-mail addresses on “TO” field, even separated by comma, the system returns me the red gear. So, when I bend to these issues, the message goes faster. Can somebody help me, specially with variables e-mail body? Thanks for the nice free system!