mjlim/dropbox-android-sync-sdk — pull request #1 by vishaldeo89 (2014-04-24 06:40:44+00:00)
Title: Only one small modification at line 69 ...

mDbxAcctMgr.startLink(this, REQUEST_LINK_TO_DBX); in place of this use below and it will start to work....
mDbxAcctMgr.startLink((Activity)this, REQUEST_LINK_TO_DBX);
as mentioned here
https://www.dropbox.com/developers/sync/start/android

public void onClickLinkToDropbox(View view) {
mDbxAcctMgr.startLink((Activity)this, REQUEST_LINK_TO_DBX);
}