There are a few possible reasons may cause this problem:
Firstly, it is likely that the printer head has gotten dirty, please clean the printer head.
Secondly, the label paper is in poor quality, you have to get labels in better quality.
Thirdly, there is dirt on the label surface, you have to keep the labels well.
Finally, rarely occurs but possible, it is possible that something has interfered with the printer driver or wrong driver is manually selected. Please uninstall AOBIO printer driver, restart your computer, and install the newest AOBIO driver available on www.AobioPrinter.com.