"k90" has the following errors:
Could not set value 'but nobody replies.\" "' - Missing quote character (")

I was working through the tutorial when I got this. I tried deleting 'say' (commands), and tried 'undo', but to no avail. Can anybody help me?

When using expressions there needs to be an even amount of quotation marks used. The error you are getting is telling you that there is an odd number of quotation marks.

When you are using the "print a message" script there are two options in the drop down box. One is message which prints everything exactly as you write it. The other, which the tutorial is getting you to use in this case, is an expression. With expressions it won't just print exactly what you type, it will print strings that are stored somewhere else. In the case of the tutorial example:

"You say \"" + text + "\", but nobody replies."

the + text + bit is you telling Quest to print out whatever text the player typed in. When using the expression mode however, using the quotation marks tells quest to print this bit directly as you have written it. If there are an odd number of quotation marks, it sees the first one and thinks "right, I have to start printing the following letters here" but never reaches the next one telling it to stop.

Finally, the backslash is used to tell Quest that this ISN'T a quotation mark it should take any notice of, but one that should be printed like any other character between the two quotation marks.

So looking at your error, it looks like you've either got a backslash in front of a quotation mark, meaning quest doesn't realise that it's there to mark the start or end of what you want to print, or you have missed out a quotation mark somewhere else, likely before the word "but."

You need to have the quotation marks stop and start before and after the + signs as well, because they're there to tell Quest that you want it to print these 3 things next to each other in a line. Your saying, first print this text between these quotation marks (You say ") AND THEN print whatever the player has entered in place of the word text AND THEN print this last thing written between these quotation marks (" but nobody replies.)

Hope this helps.

But I can't find this expression anywhere, I have deleted it. Yet somehow the game still thinks it's there. I can't change it if I can't find it.

I have deleted the command 'say'.

I don't think we'll be able to help without seeing the file. If you could attach it here, that would help.

Another avenue to pursue: switch to code view and search for the text mentioned the error message. That will show you where it is.