50+ queens have problems in hosiery (7)
I believe the answer is:
ladders
'problems in hosiery' is the definition.
'50 queens' is the wordplay.
'r0' becomes 'l' ('L' can be a synonym of 'r0').
'queens' becomes 'adders' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'l'+'adders'='LADDERS'
'have' is the link.
(Other definitions for ladders that I've seen before include "Climbing aids" , "they help people to get up" , "Hose runners" , "Runs in hosiery" , "Climbing devices" .)