Same problem here ...
After getting to the Reaper's coast I'v first met with Tarquin (after defeating void scam at the bridgekeeper house), and accepted his quest about artefact.
Then I'v met with Jahan, and traveled to the bloodmoon island, accepter the Advocate quest, killed black ring scam, then killed the Advocate.
Back to Jahan, found archive, where I'v got second part of Anathema and learned demon's name.
Then on my way back (at that point I'v already had 3 source points) I'v did the ritual for the second time in the Meistr's house. I'v killed Ryker, have tablet to the Almira, then fetched first part
of Anathema. After that I'v talked to Tarquin, gave him both parts of the sword and agreed to wait for his tinkering with it.
After that I'v done the remaining quests on the Reaper's coast, and traveled to LV to go to the nameless issle - but the Tarquin did'nt make it.
The problem seems to be related to the order of getting anathema parts, as my friend also play this but he first got the first part of anathema, then talked to Tarquin and then the got the second one, and Tarquin is on LV.
