I have the same thing happening on Windows 10 with the most up to date version.

Adding `s= replace (s, "\\", "%");` to `cache_file_name` in `new_style.cpp` removes the error message and saves to a cache file, but the local style file is still not loaded. The contents of the local style file are not present in the cache.

There seem to be an additional problem with the function `exec_use_package` in `env_exec.cpp`, possibly also `env_exec.cpp`. There, the file's parent directory is added to the url `styp`, but on Windows paths of the form "C:\Users\..." are interpreted as a combination of paths "C" and "Users\...".

I believe `url_system` needs to be used here before adding a directory string to a url.

When I try to open a .tm file on Windows that has a local style file (i.e. a .ts file that is located in the same directory as the .tm file), I get a cache error like the following:

Save error for C:\Users\jeroen\AppData\Roaming\TeXmacs\system\cache\__generic__C_\Users\jeroen\testing__, No error