I am not sure about LT, that usually comes with its own limits as part of the interpreter's working.
In OC, are you using
int Worksheet::ExportASCII(LPCSTR lpcszFilename, DWORD dwCntrl, char cSeparator = '\t', int nR1 = 0, int nC1 = 0, int nR2 = -1, int nC2 = -1);
That will then just follow standard OS limitation on path length.
CP