Hello
PDN20.dll is part of the palm desktop, it looks like your palm desktop is corrupted, I'd recommend that you uninstall palm desktop and related programs entirely from the computer and then restart it.
run palmdesktop setup from the disc or find the correct one for your device from here
http://kb.palm.com/wps/portal/kb/common/article/33529_en.htmlIf you still get the port is in use, make sure you turn off any related palm programs that might be running on the computer, made by palm or not, something might be trying to use the palm and preventing the sync, but the dll error definitely points to a corrupt installation and re-install should fix that.
What else to try? If you have another machine in the house install palm desktop there and see if it syncs there normally, if it does, then that confirms that something is going on on the other machine.