Seems the ports you need are good to go...
Your version of Mono isn't listed on the OpenSimulator site as an OK version (actually, the list stops at 4.4 and you state you have 4.42). I wouldn't expect that to be a problem but with Mono's history of "this ones great, this one isn't". I wouldn't totally rule it out as not a problem unless you're sure you haven't updated it since the grid was last running. Or if someone else could verify that they've used 4.42 without issue (I have not), or if you're running other simulators and all is well with those.
With MySql I'd verify that the user has and is accessing the DB with all the privileges it needs. If that is all OK, I'd create a new db (using the same User_ID) and launch the robust with that new db (current configs) (just to verify that a corrupt db isn't the issue). If that builds and adds all the tables and appears to be running normal, your User_ID and the communication between OS and MySql is fine. That leaves a corrupt db which may
or may not be repairable.
If the new DB doesn't build (using your current configs) I'd swap the config to a default version with only the addresses and ports adjusted but with as much of the rest of it as default as possible. If that launches and runs fine I'd start looking into your config files.
I'd also consider downloading a fresh copy of the same version of OS you are using for testing, leaving it in it's default config (HGStandalone with sqlite db) and see if that launches
and runs fine (I'd swap it's listener to 4002 and first region 4003 just so you don't have to open 9000,9001 and to verify that 4002 and 4003 are passing proper). If it doesn't, I'd suspect Mono, if it does, then I'd think mono is fine. I'd shut down and switch the db from sqlite to MySql and try it (still HGStandalone). If that doesn't pass, it's a user access or
privilege not given to the db user assigned or communication between OS and MySql. If it does run fine, I'd switch to grid mode and try to launch the robust (current configs) with a fresh db. If that runs fine, then I'd suspect the old db of being corrupt but I'd swap the db to your current one and see if it launches with the fresh copy of the software. If it does,
perhaps the db is fine but the old software has gotten whacked somehow. If it doesn't, I'm back to a corrupt/in need of repair db.
-Knowing Linux users like to reboot every decade or so, I'd do a fresh reboot if you haven't in a while. A clean socket is a happy socket.
-I assume you are using the address you gave me and not a DNS service for your domain. If you do, you might verify that it has your current address and resolves back to your pc.
-I'm assuming you haven't updated the os software since last it ran. But one thing I see so many people do is that they will update the OS software and throw the old config files in it
(lazy bones!). This can lead to all kinds of whack depending on what has changed version to version. The configs and OS version should match.
And boy oh boy, I'm running out of thoughts. I hope one of these turns out to be the problem! I do appreciate that you left Robust running just for me.