The problem is with Bitstamp because they are having a technical issue in processing deposits. See quoted tweets below for more accurate information :
STATUS: We detected a technical issue with processing bitcoin deposits. In response we temporarily halted BTC deposits and withdrawals. LTC, XRP, ETH and BCH transactions are unaffected. We apologize for the inconvenience.
UPDATE: The issue is non-security related and affects small number of users who created new bitcoin deposit address between Jan 25 4:39 PM and Jan 26 3:52 PM UTC. Our tech team is working on the solution.
To get timely updates about the issue, check their twitter account regularly.