Text queries within nested IF formulas to provide required output

Attempting a formula which is quite possibly beyond my excel knowledge!
I have a cell which showes either 3 options - Full Disposal, No Disposal, Part Disposal. I am attempting to check further cells depending on the initial value of the 'Disposals' cell.

Formula -

'=IF(AND(ISNUMBER(SEARCH("Full Disposal",X42)),V42<0),"Error",IF(AND(ISNUMBER(SEARCH("No Disposal",X42)),V42<0),"Error",IF(AND(ISNUMBER(SEARCH("Part Disposal",X42)),V42<0,U42<0),"Error","Okay")

If cell contains 'Full Disposal' & other query is true, show 'error', else check for other two types of disposal rinse and repeat.

I think where i am going wrong is with regards to whethther the ISNUMBER(SEARCH) is providing the correct response to work?

Any help much appreciated!
Thanks