I had this exact same problem an a standalone 2010 unit that was a server and POS till. No other clints. There were 2 printers, an IDN TM-U220 for coffee and a Serial TM-T88. Everything worked fine. Receipts printed correctly etc. Failure came when trying to print the reports. Have you checked that there is a default printer setup for reports in RESTAURANT TAB? For the till, is there a printer selected for REPORTS in DEVICES\WORKSTATIONS\?
I couldnt find a fault and a colleague did a clean installation ad the same problem, then by the end of day it just worked and he didnt know what he did. All I could think of was that the System default printer, the system requires rebooting to load that.