I am running PageLines Lite Edition and WordPress 3.9.2 with no plugins. (I took over maintenance of a web site from a previous person at the beginning of the year and have no prior experience with either WordPress or PageLines. I have searched the forums for a solution to my problem with no success).
Everything has been fine until 2 weeks ago (close to when WordPress updated) when I found I was unable to insert a media file when editing a post. I click on the "Add Media" button, followed by the library tag and the little circle simply spins forever. If I try the upload file tag, and drag a file in, it switches to the library tag and appears to work but then I get the message "An error occurred in the upload. Please try again later." However, when examining the library from clicking the main side bar (ie. not within a post), eveything is fine - the file is there, plus I can see all the media files and even upload with no problems.
The WordPress forum suggested switching to the Twenty Fourteen theme, which I did and everything works perfectly, so I guess the problem lies with some incompatibility with PageLines and the new WordPress.
I really don't want to switch to an alternate theme, and hope someone can shed some light on my problem.