This warning indicates that MATLAB is trying to add directories that seem to exist, but cannot be added to the search path. There are at least two situations when this might occur:
1. If you have added a removable media source, such as the A:\ drive or Z:\ drive.
2. If you have mapped a drive to an uncommon file system, such as the multi-version file system (MVFS) that is often used with ClearCase. Although Windows is case-insensitive, this file system in particular requires you to preserve case-sensitivity instead of making everything lowercase.
To resolve the problem, you will need to remove, change, or edit (e.g., to preserve case-sensitivity) the directory name being added. This might be happening with calls to the CD, ADDPATH, PATH, or MATLABPATH command. There are several places you should look:
1. $MATLAB\toolbox\local\startup.m, where $MATLAB is your root MATLAB location. (There should be no other startup.m files. You can check this by typing "which startup" at the MATLAB command prompt.)
3. The "Start in" path that you launch MATLAB from. You can check this by right-clicking on the icon that you use to start MATLAB, and choose "Properties". On the Shortcut tab the "Start in" option should not contain the faulty directory.
4. The preferences, which are found under the "File-->Preferences..." menu. Check each of the options for faulty directories.
5. $MATLAB\toolbox\local\pathdef.m. Note that when using the PATHTOOL or PATH2RC to save your MATLAB path, MATLAB does not preserve case-sensitivity, and forces all paths to be lowercase. The only way around this is to edit your "pathdef.m" file.