Same here, trying in a remote wifi (which worked before)
EDIT: And on home wifi. Ah but now I see that I still have B150 because 155 is not yet in the Play Store.
Try this work-around:
Initiate download and shut down Arc before it gets the chance to bring up the “Download could not be initiated” alert. Reopen Arc and you should find the new download in your Downloads list.
Hope it works for you. Worked for me!