TM-S2000
This scanner indicates errors with LED light codes on the machine.  When one of these errors is present it is impossible to connect to the machine. One of these errors is caused by being out of ink. Of note is that these scanners come with two ink cartridges. The first one may be drained filling the tubes in the machine, causing it to be out shortly after installation.

TM-S9000
The ink in this scanner works the same way as the TM-S2000.  In addition, it must have receipt paper installed in order to accept connections.