Erratic add to cart button behavior

I have been using eCart (currently 4.50) for years, first with Dreamweaver 8 and now with Adobe CS4.

I just updated one of my sites, and made a brand new purchase page. I added the add to cart button. My problem is that the button does not automatically go to the view cart page. The entry is there when I do go to the view cart page.

I have seen other posts about a php server error. I will try those solutions, but I do not think that is the problem BECAUSE:

I have another site in which I created a new purchase page and everything works as it should.

The databases and shopping carts are defined slightly differently.

There is an error generated by the site that does not work - can not change headers once data is sent...

This is driving me crazy. Appreciate any ideas.

Thansk

I may have located the source of - but not the reason for - this problem.

The incorrectly-behaving included a file (the database connection file, not that that matters) using VIRTUAL. I changed it to a simple INCLUDE and the error went away and teh add to cart button showed the view cart page.

The page that behaved correctly used REQUIRE_ONCE.

Include gives a warning if it fails. Require is fatal.

The urgency has gone, but I would still be curious in any comments.

Dreamweaver will use the virtual() function to attach included files if you set the "Create Links Relative To" Option on the Local Info tab of your site definition to "Site". The problem with this is that the virtual() function is only valid on some apache servers, and it outputs a bit to the page when the file is attached.

If you set Dreamweaver to use Create Links Relative To the Document, it will use the require_once() function.