When compiling with Remix, you likely just used the oraclizeAPI import statement. However, for verifying with etherscan, you need to have the whole plaintext code there in replacement of the import statement.
Likewise, ensure you've set the exact Solc version it was compiled with. There were some updates to the Oraclize API in the last few days, so beware of that as well when copying the plain text over, you may need to copy it from an earlier commit. If you continue to have trouble, you can contact Oraclize on their gitter channel https://gitter.im/oraclize/ethereum-api, and ask someone there to verify it for you, assuming you are able to provide the exact code and compiler you deployed it with.