MapleSEA (error code:6) The handle is invalid.

This error code appears on MapleSEA v106. Here is the viable solution.

Try this...
After full install 1.06 client, don't run it yet.

Download manual patch v1.06.1~1.06.2 and save it to the folder where you have installed maplestory, typical location is "C:\Program Files\WIZET\MapleStory"

Right-click the MaplePatch01062.zip that you've downloaded and select extract here, when prompt to overwrite current file, answer 'Yes'.

Now you can enjoy your new install maplestory.

Hope this help solve your problem.