Try firstly to copy it on a variable and then use that variable on the email body
I think that this error is a product limitation.
I resolved this error adding the number of Repeating Sections I need into the form and then save it (in New Mode). Then return back and add the fields and images associated (in Edit Mode). You need also turned on Recalculate formula on view mode for the image control.
To do it in the same form page, I created a workaround including a SAVE AND CONTINUE button. In other words, when I open the form in New Mode and after clicking in this button, the form turns to Edit Mode without exit the page. So, the error disapear. An important hint: You need to define as default an number of Repeating Section rows inside its setup, for example, 5 rows limited to 5 rows too. Above the limite pre-determined the form will show the same error as before.
Special Thanks to Prasanna Sathyamurthy