The Linux kernel includes a driver for Moxa serial cards.
In kernel version 3.2.0 (Debian Wheezy) it works OK.  The card is detected,
the mxser.ko module loaded, and the ports can be opened and used.
Tested with card Moxa Technologies Co Ltd CP104U (4-port RS-232 Universal PCI)

On the kernel distributed with Ubuntu 14.04 LTS I noticed that the same driver
detects the card, it appears in the module list, the I/O ports on the card and
its interrupt are registered, the devices created in /dev, setserial -bg shows
them as 16550A UARTS, but when an open is attempted the user process hangs in
an interruptible sleep.

Moxa offer a driver for download on their site, and when it is compiled and
installed everything is fine again.  I notice that it is full of conditional
compilation constructs that trigger on kernel versions, and that apparently
changes were made at least in 3.4 3.7 and 3.9 that made it necessary for them
to make changes, and probably similar changes have been made in the kernel
tree itself that have not been tested against actual hardware, and now it is
broken.

I realize that I do not provide very detailed information and it will be
difficult to work from this, but maybe someone with more detailed knowledge of
the changes in the driver interface has an idea what can be wrong.