diff --git a/Common-Errors.md b/Common-Errors.md
index dcb1b76..43083d6 100644
--- a/Common-Errors.md
+++ b/Common-Errors.md
@@ -32,7 +32,10 @@ This usually happens when a raid takes longer than the **IntervalMinutes** you'v
 Your settings.general.json file is likely missing a comma after one of your settings.  You can also use a [JSON validator](https://codebeautify.org/jsonvalidator) tool to check for other errors.
 
 ### Expected keyword (True, False, and, or) but found...
-This means you are using a buy/sell FORMULA in your PT settings, but PTM cannot parse your formula correctly.  Please ask on the PT discord to make sure your formula is correct.  If it is, but you still get this error be sure you are using spaces between all your arguments:  eg., "(A  &&  B)  ||  (A  &&  C)"
+This means you are using a buy/sell FORMULA in your PT settings, but the logic of your formula is incorrect.  Please ask on the PT discord to make sure your formula is correct.  If it is, but you still get this error be sure you are using spaces between all your arguments:  eg., "(A  &&  B)  ||  (A  &&  C)"
+
+### Empty expression
+This can occur when you are using a buy/sell FORMULA in your PT settings and a negation symbol before one of the strategy labels.  For example, (A && B && !C).  For PTM to correctly parse this formula, the strategy with negation should be enclosed in parenthesis like this:  (A && B && (!C))
 
 ### Dashboard (top) update failed!
 You can find more information about this error by using the url:  http://localhost:8000/_get/DashboardTop  (change the port to match your PTM port.