Module 'gmp' already loaded - error

I've been trying to get Grav up and running several times but I keep getting this same error. I've used the Grav core, which works up until I use the command line to install the admin plugin. Same problem when using the Big Picture skeleton or the Grav+Admin package.

This is what grav.log says:
[2016-09-29 05:57:26] grav.CRITICAL: Module 'gmp' already loaded - Trace: #0 /home/timchurc/lisa/vendor/filp/whoops/src/Whoops/Run.php(363): Whoops\Run->handleError(32, 'Module 'gmp' al...', 'Unknown', 0) #1 [internal function]: Whoops\Run->handleShutdown() #2 {main} [] []

And here's what I get when using the Grav+Admin package.
Grav error

If using Grav Core and manually installing the admin plugin, or using the Big Picture skeleton, I get the full screen 'Crickey! There seems to be an error..." page with a lot more details.

I really don't know what I should do. I've looked in /home/timchurc/lisa/vendor/filp/whoops/src/Whoops/ and Run.php does not exist. All files have come straight from Grav's website.

Thanks for any help that can be offered.

I'm not a Grav developer, so maybe there's something Grav specific. A google search gets me results like this. Not knowing more about your environment, it's hard to say.

Yeah, I came across that page, too. I thought I might ask here before bugging my web host just in case it has nothing to do with them. I'll open a ticket with them and see if they know what might be going on. Thanks, Perlkönig.

No clue what gmp is, but sounds like a problem with your PHP setup. Grav doesn't use it that I know of :)