I am having issues with LR4 stopping the export process using the jf Zenfolio plugin on files larger than 20 MB. Even when I select "upload all" it still pauses on each large file. This is making my usual exports take much longer as I have to babysit the upload.
Did you contact the author of the plug-in? Friedl's plug-ins have all sorts of additional logging, and he'd be the best person to know if there was a new problem in the latest SDK. Since the SDK docs have not been updated, plug-ins made for Lr 3 or earlier may continue to work, but there may be some subtle change that he is unaware of at this time.