This is just a guess, but do you have a matrix type modifier in the project and have you tried to apply it before exporting?

Go to RedXEye's Github and check to see if there has been an update to SourceIO since Blender 3.1 was released. If there hasn't, post your error via the issues link on the page. The Blender 3.1 update may have broken the Add-on code and may need a fix.

Edit - FYI: I have read that there is a new pre-release of Blender Source Tools which kind of indicates that the coding in 3.1 Update is causing problems in that Add-on as well, so, I would suspect it may be the case I outlined above.

If you're going to share a file like this, make sure you turn sharing (with anyone who has link) on. Your link says I need permission to download.

Yes it is possible to export multiple animations at once. See this image it should help you out.

https://i.imgur.com/nmQkz1u.png

If you have any questions, let me know.

Easy to do when working the code, I've done this many times myself and cursed a lot trying to find where I pooched up!!

Yup, fixed that little faux-pas and the model exports and compiles properly.

This might be your problem this flex is defined twice
(Line 293)
"DmeCombinationInputControl"
{
"id" "elementid" "ad6e1fd4-adfe-3694-988e-f5df67346b40"
"name" "string" "CheekV"
"rawControlNames" "string_array"
[
"CheekV"
]
"stereo" "bool" "1"
"eyelid" "bool" "0"
"flexMax" "float" "1.0"
"flexMin" "float" "0.0"
"wrinkleScales" "float_array"
[
"0.0"
]
},
(Line 310)
"DmeCombinationInputControl"
{
"id" "elementid" "22ae4fba-d94b-3d3c-bdcf-b5a7a8075c0e"
"name" "string" "CheekV"
"rawControlNames" "string_array"
[
"CheekV"
]
"stereo" "bool" "1"
"eyelid" "bool" "0"
"flexMax" "float" "1.0"
"flexMin" "float" "0.0"
"wrinkleScales" "float_array"
[
"0.0"
]
},

"LipsVUp" and "LipsVDn" are missing from the original script. I suspect that the 2nd instance of CheekV was supposed to be the LipsV.

Something in the Winklescales in the advanced flex script is firing this error. I switch to simple shapekeys and the model exports.

Check your code for syntax of the advanced flex code and also look for missing {} or "s

Blender 2.79 requires BleST 2.10.2 to work. 3.1.1 is for 2.80 and above.

2.10.2 can be gotten here.

https://steamreview.org/BlenderSourceTools/archives/

Doesn't work how, installing, when trying to export, when trying to import, etc??
What error messages are you seeing?
What version of Blender are you trying to use it in?

Just saying what you did is such a broad spectrum. You need to be more specific.