Don't forget that the version which works with 1.5.4 isn't the same as the one which works with 1.6.0 and higher...
Try to install the one on my extension site (even it's said that it's 1.6.0 compatible). The problem is probably due to spelltest.dll.
Mozilla/5.0 (x11; U; Linux x86_64; fr-FR; rv:38.0) Gecko/20100101 Ubuntu/12.04 K-Meleon/76.0
Mail : alain [dot] aupeix [at] wanadoo [dot] fr
Ubuntu 12.04 - Gramps 3.4.9 - Harbour 3.2.0 - Hwgui 2.20-3 - K-Meleon 76.0 rc