invisible arrows using xypic have zero length

Thanks again for supporting xypic (unless it causes a significant problem, of course).

I've prepared a latex file including several xymatrices with ar@{}, as well as the corresponding compiled pdf file (in which the invisible arrows are looking perfect). All of the xymatrices in the file produce the error on CodeCogs.

To what email address should I send these files as attachments?

Thank you very much for considering this problem!

VC1