I've been trying to purchase a Barcelona Articket online using the website mentioned in Rick Steves' Barcelona guide (www.articketbcn.org). Every time I try to purchase the ticket, though, the website won't allow me past the screen where I select the number of tickets I want. Instead, I get a message that "the sessions haven't been selected." I can't figure out what this means. Any suggestions would be most appreciated!
Did you set the "How many of you are there?" counter for the number of Artickets you want to buy? I had no problem getting to the screen for entering a credit card number.
Sometimes a website doesn't work properly with all types of devices and all browsers. I tested this on an Android tablet. You might try different hardware, or a different browser.
While skimming through the FAQs on the website, I was reminded of the unbelievably crowded conditions I faced at the Picasso Museum in 2016. I generally find audioguides useful at art museums (though they will add time to the visit). I especially recommend the audioguide at the Picasso Museum, because getting close enough to read the labels beside the paintings can be very, very difficult.
The FAQs (which I thought were very useful) mention that during free-entry periods there is no special-access point for Articket holders, so you should try to avoid those times. Normally, I'd expect conditions to be worst at the Picasso Museum (that's a given), with the other two likeliest to have a back-up at the entry point being the Miro Museum and MNAC.
The FAQs provide a specific address to use for entry to the Picasso Museum at non-free-entry times. The regular entry point is often an utter zoo, so pay attention to those instructions.