Hi,
Would you let us know which add-on show 603 error. Can you find this add-on from https://creative.adobe.com/addons/my_addons (even it is a free add-on)?
And we need following informations:
* Your device (windows or Mac)
* How did you use Extension Manager to install that add-on? Where do you get the zxp file? Did you install that add-on from Adobe Exchange Panel?
1. Create a file called exmancoreliblog.yes and copy it to
Mac: /Users/<name>/Library/Application Support/Adobe/Extension Manager CC/Log/
Windows: C:\Users\<name>\AppData\Roaming\Adobe\Extension Manager CC\Log
2. Restart Extension Manager and reproduce your issue
3. Send us ExManCoreLibrary.log file in that log folder to exman.beijing@gmail.com