This error occurs when trying to print using the PS-9000 using an incompatible version of P-touch Editor.
To print with QL-500/550 using the PS-9000, you need version 4.1.101 or later of P-touch Editor.
Check your P-touch Editor version using the [HELP] – [About...] menu.

[For P-touch Editor Ver. 4.1. 100]
P-touch Editor V4.1.100 is not compatible with the PS-9000 print server.
Download and install the latest version from the Brother support website.

[If you are using a later version of P-touch Editor than Ver.4.1.101]
If other users are printing to the QL-500/550, this message may appear.
Wait for a while and then click the [RESUME] button on the print monitor display.

Also, if another user's print job was stopped due to the error, this message may appear.
Turn the power off on the QL-500/550 to cancel the print job, and click the [RESUME] button on print monitor display.