I believe I had a similar issue. Mine seemed to be related to the fact my RoboHelp was installed as part of the Technical Communication Suite (TCS2).
If your install is similar to mine, you will likely discover that you need to add the tools in manually. You should find them in the following (or similar) location:
?:\Program Files\Adobe\Adobe Technical Communication Suite 2\Adobe RoboHelp 8\RoboHTML
I think that before I amended the path it was incorrectly pointing to:
?:\Program Files\Adobe\Adobe RoboHelp 8\RoboHTML
( ? = Installed drive letter. Often C. )
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