[function.opendir]: failed to open dir

Hello,
Iam new to drupal and getting some errors. I couldnt get a clear answer from google/this forum, so I'm posting here.
I have my modules in .\sites\all\modules. I have just added the module simplenews and all is working ok. Now iam adding the module mime mail but get the following error. How can i solve this? And what is going on?

•warning: opendir(sites/all/modules/mimemail5) [function.opendir]: failed to open dir: No error in C:\Inetpub\wwwroot\Snoeken\includes\file.inc on line 888.
•warning: opendir(sites/all/modules/mimemail5) [function.opendir]: failed to open dir: No error in C:\Inetpub\wwwroot\Snoeken\includes\file.inc on line 888.

regards, Matthijs