Resolution:
When using LiveCache on a Windows system, there is a key length limitation of 256 characters. This includes the full path leading to the base directory where keys are stored on the Manager. This is defined on the Manager Configuration page in the Miscellaneous section, in Base Directory.

Note that as a workaround, you can change the base directory to another location to enable longer keys. For example, setting the base directory to c:\lc would enable the use of keys up to 250 characters in length.