I was able to fix the problem. It took a lot of care to eliminate *every* file that referred to the old blockchain download. Apparently my download had forked. Since I use linux, it was stored in a file in my .bitcoin directory. I hadn't erased everything before, when I tried to re-sync, so it encountered the fork again. So I erased the .bitcoin directory as well as the entire software download (except my wallet, which had my coins, of course, and all the files related to the wallet.)

Then I downloaded everything from scratch and re-synced and it works fine now.

I hope this helps.

(Changed the subject to include XMR)

I'm sorry. I don't understand your reply.

I've been mining monero for a couple years with no major problems, but I got this error a few days ago:

ERROR /DISTRIBUTION-BUILD/src/cryptonote_core/blockchain.cpp:3401 WARNING: local blockchain failed to pass a MoneroPulse checkpoint, and you could be on a fork. You should either sync up from scratch, OR download a fresh blockchain bootstrap, OR enable checkpoint enforcing with the --enforce-dns-checkpointing command-line option

so I synced from scratch (took 2 days) and today got the same error at the same point in the sync:

2017-Apr-18 13:23:23.433588 ERROR /DISTRIBUTION-BUILD/src/cryptonote_core/checkpoints.cpp:106 CHECKPOINT FAILED FOR HEIGHT 1288616. EXPECTED HASH: <875ac1bc7aa6c5eedc5410abb9c694034f9e7f79dce4c60698baf37009cb6365>, FETCHED HASH: <1e6b1019968d4a33b281ab70d83947bc051ac952f26dd2693c427b04d82151fe>
2017-Apr-18 13:23:23.433803 ERROR /DISTRIBUTION-BUILD/src/cryptonote_core/blockchain.cpp:3401 WARNING: local blockchain failed to pass a MoneroPulse checkpoint, and you could be on a fork. You should either sync up from scratch, OR download a fresh blockchain bootstrap, OR enable checkpoint enforcing with the --enforce-dns-checkpointing command-line option

The main problem for me is that monerod is running and has been stuck at block 1288638 for more than 24 hours. I'm running 0.10.3.1

What do I do to fix this?

OK. Got the problem solved. Had to use the new 0.9.1 blockchain and bitmonerod, of course, and my old wallet file refused to work with the new blockchain and new bitmonerod, (and the 0.8 bitmonerod wouldn't work with the new blockchain, of course). Every time I tried a transfer (to move funds to a new wallet) the transaction would be refused by the network. But finally tried transfer_new and it works fine. I was able to move funds a little at a time to a 0.9.1 wallet.

Thanks to everyone for the advice.

I'm using wallet 0.8.8.6, and tried to deposit 200 XMR in Poloniex (my first deposit ever).
Got response from my wallet:

Your transaction needs to be split into 3 transactions. This will result in a fee of 0.015000000000. Is this okay? (Y/Yes/N/No)Yes
Money successfully sent, transaction <76f1d4f51724c0df3e7b6dde2a91fa370bd79d7633d01ca4159eb1aafb55fbfc>
Money successfully sent, transaction <189cb20ecbfb985f8c1c3db4e94b43110cf6b9c9ef46db149321a2643760e199>
Money successfully sent, transaction <85281a3675972e587360aba73e510cffb4d56ea4e635020962efc4b2541358b3>
They are not showing up.

Recently my wallet has had a lot of transactions in the blockchain that are like this:

2016-Jan-22 21:40:51.167059 [P2P8]ERROR
Desktop/Coin/Monero/bitmonero/src/cryptonote_core/tx_pool.cpp:98 transaction is too big: 32176 bytes, maximum size: 24400
2016-Jan-22 21:40:51.168943 [P2P8]Transaction verification failed: <24433464e4af8e851a0bcac39fd127ab63fc6a9818ace08a0a454f8ebd136cb7>

How do I get the 200 XMR back? If I upgrade to 0.9.1 will that help?

Thanks,
dpb53