I can't open files using just the filename from the current directory. Output below:
D:\Dropbox>fossil open test
C:\WINDOWS\fossil.exe: SQLITE_ERROR: no such table: vvar
C:\WINDOWS\fossil.exe: no such table: vvar
REPLACE INTO vvar(name,value) VALUES('repository','D:/Dropbox/t

If you have recently updated your fossil executable, you might
need to run "fossil all rebuild" to bring the repository
schemas up to date.

D:\Dropbox>fossil open .\test
C:\WINDOWS\fossil.exe: SQLITE_ERROR: table vvar already exists
C:\WINDOWS\fossil.exe: table vvar already exists

If you have recently updated your fossil executable, you might
need to run "fossil all rebuild" to bring the repository
schemas up to date.

D:\Dropbox>fossil open D:\Dropbox\test
C:\WINDOWS\fossil.exe: SQLITE_ERROR: table vvar already exists
C:\WINDOWS\fossil.exe: table vvar already exists

If you have recently updated your fossil executable, you might
need to run "fossil all rebuild" to bring the repository
schemas up to date.

D:\Dropbox>cd ..

D:\>fossil open Dropbox\test