Not a lot on Android devices on the subject,but what little I've found is it's typically a WI-FI Calling error of sorts OR an error that pops up if you've unlocked a carrier device & use a SIM Card from a different service provider that does not support WI-FI Calling (Or MAYBE vice-versa,a SIM Card from a WI-FI Calling provider in a phone that may not be able to support it).

http://androidforums.com/threads/i-keep-getting-er05-invalid-sim.862394/

http://thedroidguy.com/2015/11/ro5-...-s6-more-connectivity-issues-1052400#Problem1

https://www.ifixit.com/Answers/View...+when+recieving+an+"Invalid+Sim+Card"+message

So,at least it doesn't seem to be a hardware (device) issue.
I'd contact your service provider,especially if it's a carrier-branded phone & the SIM is the same.
Either way,a call to your service provider is in order & worse-case scenario (hopefully) is starting fresh with a new SIM Card.

On non-Android devices,a bug with WhatsApp seems to be some what prevalent.
If you're still coming up empty,the most prevalent Google search seems to involve i-Phones.
Take your pick of search hits on that,a lot to choose from.

Please keep us posted on your outcome.