I agree with Michael, you have to send the print job using the printer set up on the local PC, not the "via logmein" printer.
John,
Please amplify how this applies if the local computer (the one with AC on it that I'm controlling) is windows, and I'm trying to print to a network printer from that windows machine.
The Mac that you are using as the remote needs to be using Firefox 3 (Firefox 4 only has a beta plugin), not Safari or Chrome. This is because Firefox uses the Java-based LogMeIn Remote Control protocol, which is the only mode that supports printing using LogMeIn on remote Macs.
The target or local PC must have LogMeIn Pro2 (not free), and has to also be set to the Java mode. To switch to this mode on the target PC, go to Preferences > Remote Control settings, and switch Default Remote Control from ActiveX to Java. As an extra benefit, the Java mode is a bit faster in low bandwidth, in my experience.
The above setup is from memory; I haven't actually used the remote printing from Mac to PC via LogMeIn for over a year, since I began using Hamachi. I'll try this from my home Mac to my office PC later this weekend and see if I can reproduce your issue.
