There was a recent update for HTML Coin v2.0.1.0, so you need to update your wallet because of a hard fork.
Release Notes:
*** MANDATORY UPDATE ***
Hard fork on block 106,000, approximately Friday 13:00 GMT,
this is to stabilise the eHRC difficulty adjust.
In case you already had HTML Coin installed, you just install the new version over it (for Linux and win).
These are the commands I used under CentOS 7:
git clone https://github.com/HTMLCOIN/HTMLCOIN.git
cd HTMLCOIN/
cd depends/
make HOST=x86_64-pc-linux-gnu
cd ..
rm -Rf src/cpp-ethereum/
git submodule update --init --recursive
./autogen.sh
./configure --prefix=`pwd`/depends/x86_64-pc-linux-gnu
make
Source / Reference:
https://github.com/HTMLCOIN/HTMLCOIN/issues/21#issuecomment-361045044
https://github.com/HTMLCOIN/HTMLCOIN/issues/10#issuecomment-356208787
Both comments are from Bushstar, based on the website he is the Executive Vice-President for Technology at HTML Coin.
Be sure to backup your wallet before the update (File -> Backup Wallet). Iam writing this also as a reference to myself. Was a bit lost when installing it the first time under CentOS, the readme just says:
Quickstart
Build on Ubuntu
This is a quick start script for compiling HTMLCOIN on Ubuntu
sudo apt-get install build-essential libtool autotools-dev automake pkg-config libssl-dev libevent-dev bsdmainutils git cmake libboost-all-dev
sudo apt-get install software-properties-common
sudo add-apt-repository ppa:bitcoin/bitcoin
sudo apt-get update
sudo apt-get install libdb4.8-dev libdb4.8++-dev
# If you want to build the Qt GUI:
sudo apt-get install libqt5gui5 libqt5core5a libqt5dbus5 qttools5-dev qttools5-dev-tools libprotobuf-dev protobuf-compiler
git clone https://github.com/HTMLCOIN/HTMLCOIN --recursive
cd HTMLCOIN
# Note autogen will prompt to install some more dependencies if needed
./autogen.sh
./configure
make -j2
But there were a lot of comipiling try and error with different packages installed, the two comments pointed me to using the dependencies delivered with the source files of HTML COIN.
Running and syncing HTML Coin under CentOS 7.
EDIT: On linux I also had to remove the blockchain (under /home/user/.htmlcoin, dont't remove anything, just the chain, not your wallet.dat file!!!), and resync everything.