Cryptopia has recently instituted some changes including minimum amount of coins that can be traded and withdrawn.
For example users trying to sell a small amount of coins for Doge are receiving a message the trade must have a minimum value of 500 Doge. Previously it was 1 Doge, a 500 fold increase.
When trying to transfer the coins they can't sell out those same users are receiving a message they need to have 20,000 coins in order to withdraw their own coins regardless of whether they are willing to accept the transfer fee.
In short due to these changes some users have been transferring smaller amounts of coins to Cryptopia only for them to be 'trapped', unable to either sell or withdraw.
Hopefully all this is some kind of error to be corrected by Cryptopia. In any event if you use Cryptopia be aware of the changes before you transfer anything in.