Odd problem with checkpoints / got stuck syncing the blockchain

Hi all,

my machine running my ppc node was down for the last 3 weeks. Today I started it again and started ppcoind and got the following problem:

lambda@debian:~$ ppcoin/src/ppcoind getinfo
    "version" : "v0.4.2.0-unk-beta",
    "protocolversion" : 60004,
    "walletversion" : 60000,
    "balance" : 0.00000000,
    "newmint" : 0.00000000,
    "stake" : 0.00000000,
    "blocks" : 220302,
    "moneysupply" : 22973360.27842400,
    "connections" : 19,
    "proxy" : "",
    "ip" : "",
    "difficulty" : 508146870.18132710,
    "testnet" : false,
    "keypoololdest" : 1451337211,
    "keypoolsize" : 101,
    "paytxfee" : 0.01000000,
    "errors" : "WARNING: Checkpoint is too old. Wait for block chain to download, or notify developers of the issue."
lambda@debian:~$ ppcoin/src/ppcoind getcheckpoint
    "synccheckpoint" : "6dc637876064c6281dc5fcded4296de86b87346c437a4bea40fda541b311f144",
    "height" : 218723,
    "timestamp" : "2016-01-29 20:08:18 UTC"

That is: The last checkpoint is from around the time when the machine stopped. When ppcoind was started today, it downloaded a huge number of bocks, but no checkpoints. Eventually it stopped downloading blocks - maybe because it is waiting for the checkpoints.

The last lines of debug.log are:

version message: version 60004, blocks=222847
ProcessSyncCheckpoint: pending for sync-checkpoint 0000000000000008866c5b79f9089e6975a2e73d393149077c3529b15e4a0ef1
askfor block 2b7475ef56a49f7fc0b9   1456152755000000
accepted connection
version message: version 60004, blocks=219140
ProcessSyncCheckpoint: pending for sync-checkpoint 000000000000000437fe2384e3c561ad651bc3f610667b819b0fa58e10c1f568
askfor block 2b7475ef56a49f7fc0b9   1456152875000000
socket closed
disconnecting node
askfor tx 77bd3abe18812a2379dd   0
sending getdata: tx 77bd3abe18812a2379dd
askfor tx 77bd3abe18812a2379dd   1456152940000000
ERROR: FetchInputs() : 77bd3abe18 mempool Tx prev not found 0c0117b041
ERROR: CTxMemPool::accept() : FetchInputs failed 77bd3abe18
stored orphan tx 77bd3abe18 (mapsz 43)

Has anybody got an idea what might be wrong or how to debug this?

the log term ‘orphan’ suggests that it is on a orphaned chain ?

what if you delete the dat files and restart?

An orphaned chain 1580 blocks since the last checkpoint that started about the time when my machine disconnected from the network? How unlikely is that?

I guess ‘orphan’ in this case means an transaction that references a block that we haven’t seen yet…

what if you delete the dat files and restart?

This would very likely fix the problem. However then we would have very little chances to figure out what went wrong and fix the problem. A software like ppcoin should be very robust, so lets fix problems instead of working around them!

It’s just: I have no idea where to start looking for this one…