Well, seems like it's not finding a variable? Are you sure the variable is actually there? It might also be it needs to be set to public or something to be accessible? I'm not sure. The error is presumably in WriteToFungus.cs:114, but I have no idea what that does :)
When I've encountered previous issues with this error, the message is always 'Variable <name> not found' so I'm a little perplexed - it looks like Playmaker has some variable it's trying to gather from Fungus, but the variable itself is unidentified, so I'm not exactly sure. Doesn't appear to be affecting the application in any way though.
Is the variable you try to access a "global variable" in Playmaker? I think only global variables can be referenced using the playmaker fungus actions.