Your problem is likely the same one that me and others are facing (see this thread: Staking problems within NNS app). In that case, dfinity devs have made the following announcement:
A few users have reported issues when trying to stake neurons.
IMPORTANT: No funds are lost as all transactions are immutably recorded in the ledger!
We understand the problem and we are working on a mitigation. All users who have attempted to stake neurons will either have the transaction reimbursed or their neuron staked.
No further action is required on your part. The issue will be resolved within the next few days.