Depending on your OS, colons and backslashes aren't permitted in filenames. That looks like the problem. I'm guessing you're using windows as it appears to be complaining about the "slashes"
Try this: "Export "& Substitute(Get(CurrentTimeStamp), "/", "-") &".csv
I haven't tested this expression, but am fairly confident it will work.
(You may need a "getastext" function to wrap around your timestamp.)
I'm actually in OSX. I'll try doing some text formatting and see if that helps.
So it turns out that it was both the ":" and the "/" causing problems for me. Intersting that this was the case, I wouldn't have thought it myself.
The getastext wasn't needed; get(currenttimestamp) returns as text.
I knew that ":" on a mac and "/" on windows marks the delimitter between enclosing folders in filepaths and thus are not permitted in filenames. That's what first caught my eye in your original post. A new fact to me that "/" aren't allowed on the mac side as well.