matching an image to a reference image

[streicher]

Hi,

I want to match (i.e. rotate and resample) an image to a given reference image without any co-adding.
For this, I have extracted and saved the header from the reference image. But still, when I run swarp, the result is rotated with respect to the reference image; the image size and pixel scale seem to be correct.

Does swarp recognize CROTAx keywords?
Is it a problem, when the image axes (x,y) are not parallel to the coordinate axes (ra,dec)?

What else could be cause the problem?