Disapearing Report Formula's

when i create a formula, it works, no errors, i use it a few times on the report, i can SEE it in the field browser, yet when i go to draw a graph on it, its not listed as an option.

i went back to see an old graph that also used this formula, and sure enough it was locked in there in the "on change of" section. yet when i clicked the "Order" button, up popped the dialogue without my formula preselected, and wasnt listed as an option!

if i create a new formula, copy the text across and then save it, i can use that formula for like the next 10 mins, and then the same thing happens all over again.

obviously i cant continue like this... i might try and post this on the cystal board aswell...

(Note: this isnt occuring for ALL of my formula's, they just seem to suddenly drop out and never come back (although still listed in field explorer))