You must completely Uninstall Plarium play from you computer  first every bit of it  including from C: drive  empty your Recycle bin  any past downloads of the app from your downloads area  all of it then restart your computer and do a check to be sure it's all been removed.

Then try reloading the App it should work.

I had the same thing last week

When I go to uninstall it gives the option to "Keep all data (for reinstallation)" - are you saying I should not tick that? I am afraid to lose all progress I have made. This has only been a problem for a week or so (since the last update??) so am reluctant to take the drastic step of deleting everything.

No you can click that portion just remember your sign in details of your accounts (I hope you have them written down.) Just in case you need them in the future.

Decided against such a drastic step, instead opted to wait for a "fix" and today all appears to be OK! Thank you, though, for the advice.

Glad your Back  I'm thinking you must of had Internet Service Provider issue. I'm glad they got you back in now. :)

Afraid the ISP cannot be blamed here - there was a new update pending, shown by the litlle red arrow, and installing that cleared all the problems. Others in my league - from different countries - had similar problems, so could not be ISP.

as long as your back on that's what matters :)