Okay, first things first. What type of calculation are you attempting to do in the query? Are you calculating across multiple fields? Please provide a little more information about the calculation and the table structure if any the calculated fields are based upon.
You can also use queries to calculate fields from several tables, perform regular calculations, etc. You can also perform calculations inside a report based on grouping and that may be easier, but I need to know a little more about what the calculation is and the underlying table structure.
Is your field called HomeSum or HouseSum? You have it written both ways in your question. Try it without putting [ or ] around your constant.
Thanks for your reply. Yes it should be HomeSum not HouseSum. But that wasnt my problem. I tried it without  around my constant, but I still got a "syntax error in query expression 'tblHomeProp.0.011937*[HomeSum]' "
I have chosen (in the "table" field located under the expression) the table that contains the field "HomeSum". I assume I need this. This causes the syntax error. When I leave the "table" field blank then there is no syntax error. Whats the story?
Check out this little sample I just made. Is this what you are trying to do?
Also, if you are creating the expression, then the table field should be left blank. The query will not add this data to your table nor is the new field you are creating in your table. It is basically just a display only look at it so you do not need to put in anything in the table field.