Problem

Solution

User dictionary; the 'Add' button changes to 'Adding...' when it is clicked and nothing else happens.

This is an indicator that an exception occured during the control's attempt to write to the user dictionary. Double check that the ASP_NET process has permission to write to the file and folder specified for the user dictionary file. If unsure, try changing the path. Remember, just setting the user dictionary path to a relative path (eg. "userdict.txt") will result in a path off the Windows system folder, not the current web app folder, use HttpRequest.MapPath to map a virtual path.

Visual Studio fails to build the project sometimes and reports errors such as BC31011: Unable to load referenced library.

To do this use GACUTIL (comes with the .NET framework) in the same folder as your DLLs:
gacutil /i Keyoti.RapidSpellWeb.dll
gacutil /i Keyoti.RapidSpellMDict.dll
and then re-add the references to the project.

A license error is shown.

Ensure that the LicenseKey property in RapidSpellWeb (the control in the popup, usually) is set. Ensure that the key has no white space or newlines in it.
Ensure that the key is a 'deployment key' generated through our website, not an 'activation key'.
Ensure that the page on the server is up to date and has the key set (this is often wrongly assumed).