I had to create a test account especially for that.
Had no problems using xAbRP';Xcx{QpHk;57-
as password (no basckshles \
sign).
When I tried to use xA\bRP';Xcx{QpHk;57-
authentication failed. The fix was to use @-string.
Remember that backslash is an escape character in C# it must be escaped or @-string used:
string pass = @"xA\bRP';Xcx{QpHk;57-";