That looks like something other than the sheet Lars. "base.js..." mentioned in the error is an external javascript file Roll20 loads with the character sheets. Not sure why it's only a problem for one sheet though. As an option(depends on GM), perhaps try using the character vault and/or transmogrifier and copy your Arcanist into another test campaign and see if you still have the error there. If no errors, try deleting the character from the regular campaign and an re-import. But, first I would follow the usual Roll20 Dev/Mod tech support advice: Can you please follow Steps 1-3 of our Solving Technical Issues wiki page, taking special care to temporarily disable all browser add-ons and extensions, temporarily pause your anti-virus, and try switching browsers (for Chrome/Firefox specific issues) to see if one of those components is causing the problem. If all of that fails, please follow Step 4 , including providing all of the necessary information, so that we can further assist you. and post in the Bug Reports and Technical Issues .