Avatar - access denied

I'm getting error messages in the front-end when trying to select a gallery or uploaded avatar, is this a common issue?

You need to provide the error message. CB Gallery can be protected by CB Privacy so if you have CB Privacy installed and the necessary system actions in CB Auto Actions published it could be privacy blocking it if it's not your gallery.

The error message is just: 'Error - Access Denied'.

We don't have CB Gallery or CB Auto Actions installed on the site.

The error message is just: 'Error - Access Denied'.

Where and when is it saying this? When navigating to profile edit? When trying to save your profile? Please, you need to be specific.

We don't have CB Gallery or CB Auto Actions installed on the site.

Ah, you're referring to the image gallery of an image field.

Sorry - please see below for better explanation:

1. We have enabled 'avatar' on the profile edit screen
2. When a user goes to edit their avatar, they can select from 4 options (No change of image / upload new image / select from gallery / remove image)
3. When selecting a new image (either uploaded or from gallery) and clicking 'Update' - the error message appears at the top saying 'Error - Access Denied'.

Sounds like it's mod_security or Joomla access permission issue. Contact your host and see if mod_security is enabled and if it is have them check the logs or if you can check your server logs to see if mod_security logged an exception there. If no mod_security issues I'm not sure what to suggest since the Access Denied error in Joomla appears to only apply to the authentication (login) workflows; if you've two-factor authentication enabled try disabling it as maybe the authentication check there is causing it.