After uninstalling v3 and installing v4 I received the following errors and also the JoomDOC menu entry on the 'Components' menu in the backend is missing? Didn't do anything strange - just a simple uninstall old, install new. CAN get to the component by adding the appropriate token to the URL (so the component is working) BUT the menu entry .... what's happened?

* JLIB_INSTALLER_ABORT_PLG_INSTALL_ALLREADY_EXISTS
* JLIB_INSTALLER_ABORT_PLG_INSTALL_DIRECTORY
* JLIB_DATABASE_ERROR_MENU_ROOT_ALIAS_FOLDER
* JLIB_INSTALLER_ABORT_COMP_BUILDADMINMENUS_FAILED


* Install Module JoomDOC module Success
* Install Module JoomDOC Explorer Success
* Install Module JoomDOC Search Success
* Installing component was successful.

Hello,

does the problem still occur?

Yes I'm afraid it did.

The front-end seemed to work as expected, but the back-end did not have any Component menu entry.

In the end I was forced to manually uninstall everything (filesystem + database) and have been put off from installing it again.

Hello, try to clenup database:

Delete all rows from the table jos_extensions which have in the column element text com_joomdoc.
Delete all rows from the table jos_assets which have in the column name text com_joomdoc.
Delete all rows from the table jos_menu which have in the column link text com_joomdoc.