This message could potentially appear if you upgrade to 4.5.3 or higher.

If you run into such issue, please make sure you  have done the following.

• connect via ssh to your GL appliance
• enter: 

vim /opt/panagenda/appdata/gl/config

• add the following line at the bottom of the file and save/close it

PANAGENDA_CORS_ALLOWED_ORIGINS=your_GL_URL

example:
PANAGENDA_CORS_ALLOWED_ORIGINS=https://gl-dev-01.panagenda.local

• enter:

gl start