I would appreciate any suggestions on a background tiling problem.

I am creating a semi-transparent, single-color PNG to be the background image for a
website div. I am able to create the image in Xara (using Xara 5) and the transparency
looks great once the image is uploaded and coded into the html/css.

Unfortunately, as the image tiles vertically, there is a thin (horizontal) border
between the tiles, so I don't get a smooth background. Instead, I have
horizontal lines down the page per the height of the image.

When I import the PNG image back into Xara, there is clearly a 1 or 2 pixel
completely transparent border around the image. I can't seem to get
rid of it.

I have double-checked that all borders are 0 when I export the image.
I am exporting as a PNG, "true color + alpha" for the palette.

Thank you for any suggestions. Alternatively, if anyone has an
idea for generating a semi-transparent tile for html, that would
also be great. Note that I have a top image as the
first background that is rounded, with rectangular images/tiles
that follow.