MSDN docs on FindFirstFile (the win32 API that underlies opendir) state:

-----
... Similarly, on network shares, you can use an lpFileName of the form "\\server\service\*" but you cannot use an lpFileName that points to the share itself, such as "\\server\service".

To examine any directory other than a root directory, use an appropriate path to that directory, with no trailing backslash. For example, an argument of "C:\windows" will return information about the directory "C:\windows", not about any directory or file in "C:\windows". An attempt to open a search with a trailing backslash will always fail.
-----

So, try it with a trailing backslash.

Looks like it yields the same results.

<?php
$dir1 = "\\\\matt\\F Drive\\";
$dir2 = "\\\\192.168.0.6\\F Drive\\";
$dir3 = "//matt/F Drive/";
$dir4 = "//192.168.0.6/F Drive/";
opendir($dir1);
opendir($dir2);
opendir($dir3);
opendir($dir4);
?>

Warning: opendir(\\matt\F Drive\): failed to open dir: Invalid argument in C:\Inetpub\wwwroot\ExitCareWeb\test.php on line 6

Warning: opendir(\\192.168.0.6\F Drive\): failed to open dir: Invalid argument in C:\Inetpub\wwwroot\ExitCareWeb\test.php on line 7

Warning: opendir(//matt/F Drive/): failed to open dir: Invalid argument in C:\Inetpub\wwwroot\ExitCareWeb\test.php on line 8

Warning: opendir(//192.168.0.6/F Drive/): failed to open dir: Invalid argument in C:\Inetpub\wwwroot\ExitCareWeb\test.php on line 9

"To anyone who needs to use UNC mapped drives with 
OpenDir(), if you are having a problem with OpenDir() reading 
the directory, check your permissions for the share on the 
host machine. Start with giving full permission to everyone 
(which should work fine) and then back accessability until you 
have a problem."

from bug #22153

It is not security.
I went to the Sharing tab and clicked the Perissions button for the F Drive Share. I gave Everyone full control. I also went to the Security tab and set Everyone to full control. Applied the changes, reran the script. Exact same result.

Try renaming those shares not to have that space in them,
for example 'F Drive' -> 'F_Drive'..

I redid the share to be called 'fdrive'.
Then updated my script accordingly:
<?php
$dir1 = "\\\\matt\\fdrive\\";
$dir2 = "\\\\192.168.0.6\\fdrive\\";
$dir3 = "//matt/fdrive/";
$dir4 = "//192.168.0.6/fdrive/";
opendir($dir1);
opendir($dir2);
opendir($dir3);
opendir($dir4);
?>
But I still get:

Warning: opendir(\\matt\fdrive\): failed to open dir: Invalid argument in C:\Inetpub\wwwroot\ExitCareWeb\test.php on line 6

Warning: opendir(\\192.168.0.6\fdrive\): failed to open dir: Invalid argument in C:\Inetpub\wwwroot\ExitCareWeb\test.php on line 7

Warning: opendir(//matt/fdrive/): failed to open dir: Invalid argument in C:\Inetpub\wwwroot\ExitCareWeb\test.php on line 8

Warning: opendir(//192.168.0.6/fdrive/): failed to open dir: Invalid argument in C:\Inetpub\wwwroot\ExitCareWeb\test.php on line 9

Not enough information, assuming this is run under IIS where 
this document applies:

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q189408

Hi there !

Had the same problem... but solved it :)
in fact it IS permission related...
(like sniper@php.net said)

my conf:
WEBsrvr nt5 + Apache/1.3.24 (Win32) PHP/4.3.4RC3-dev
SMBsrvr nt5

the deal:
WEBsrvr access a share on SMBsrvr with opendir()

the problem:
$d = opendir('\\SMBsrvr\whatever');
Warning: opendir(\\SMBsrvr\whatever): failed to open dir: Invalid argument in C:\Inetpub\www\script.php on line x
--`this is not a usefull warning !`

$fp = fopen('\\SMBsrvr\whatever\file.ext','rb');
Warning: fopen(\\SMBsrvr\whatever\file.ext): failed to open stream: Permission denied in C:\Inetpub\www\script.php on line y
--`hmm, hmm, more interresting...`


At this point had to investigate a bit more:
Apparently apache + php know that \\SMBsrvr\whatever exists and that it is a valid directory ressource...


Did some packet log on SMBsrvr:
WEBsrvr sends a SMB `Tree Connect AndX Request` using nullSession
SMBsrvr replies by an ACCESS_DENIED

gotcha !

SMBsrvr doesn't allow nullSession...
but why WEBsrvr tries to connect using nullSession ?
because Apache is running as LocalSystem

From MSDN:
`Windows NT - LocalSystem:
The service has limited access to network resources, such as shares and pipes, because it has no credentials and must connect using a null session. The following registry key contains the NullSessionPipes and NullSessionShares values, which are used to specify the pipes and shares to which null sessions may connect:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters
Alternatively, you could add the REG_DWORD value RestrictNullSessAccess to the key and set it to 0 to allow all null sessions to access all pipes and shares created on that machine.`

Enough blabla:
Either you allow the host of share to accept nullSessions
or you create an account with enough privileges on the apache host and when in mmc/Services/Apache/Connexion "Open a session as" - use the newly created account...

All of this is true for Apache, but it should be 'approximatively' the same concept for IIS...

a few references for this 'bug' (that is not)
http://bugs.php.net/bug.php?id=24795
http://bugs.php.net/bug.php?id=22153
http://bugs.php.net/bug.php?id=20813
http://bugs.php.net/bug.php?id=13058
http://bugs.php.net/bug.php?id=12524

attn to: iliaa@php.net; sniper@php.net
there are a lot of bug reports for this local config. problem
maybe an addendum in the documentation could be usefull...

sorry for my bad english...
/hth
/bye

dr_no