If the above error appears when you save an event please ensure that you are formatting the conditions for the event correctly by checking the below
First ensure that the value(s) entered are correct and valid and then ensure the operator is filled in.
If you have 1 value in the value field, ensure that it looks similar to this, 'Value', with single quote marks
If you have 2 or more values ensure they have a comma between them like this 'value1','value2'
If the operator being used is IN or NOT IN please ensure the value looks like this, ('value1','value2','value3')