The secure CRT string functions such as wcscpy_s() and wcscat_s() invoke the invalid parameter handler if the destination string is too small. This defaults to a fastfail that terminates with the status code 0xC0000409, subcode 5 (FAST_FAIL_INVALID_ARG).

We're using buffers sized MAXPATHLEN+1 in PC/getpathp.c, which supports 256 characters plus a terminating null. We could increase the buffer size, but bear in mind that Windows itself doesn't completely support running applications from a long path. So you may still hit road blocks.