The alternative solution I found out is to move the datepicker code from product_options.tpl to product.tpl , I moved it after the html end tag but it can be moved inside too , after that no more errors in IE7 and IE8. The same fix can be used in the default theme but in that case the code is already in the product.tpl file.
I suggest you to do that change in future Shoppica releases so that other people don’t have to deal with this issue in the future , either that or revise the datepicker inline code to make it work without bugs inside the product_options.tpl file.
I also found 2 other bugs using IE7 and IE8 , these exclusive to Shoppica , one is a minor CSS bug and happen with IE7 when you go to the shopping cart and click in “Apply Discount Code” the button “Apply Coupon” goes down , you can see it here: http://shoppica.net/index.php?route=checkout/cart , I removed “position: relative” from .s_button_1 in the ie.css file and now the button is fixed but the text still goes down , do you know what changes I have to do in the ie.css file so the text stay in place too? the other bug happens with IE7 and IE8 and is related to the “CSS3 Progressive Internet Explorer” ( PIE ) that you have used to render css3 in IE7 and IE8, ( shoppica/js/PIE.js ) and I had to use a “dirty” fix to make it work close to the way it should.