Runtime error when uploading a project

Dear Experts,

I'm having a problem when I upload unedited downloaded projects.
We're talking about Blogengine 2.8 and Umbraco CMS 6.

This is the standard error:

Runtime Error Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed remotely (for security reasons). It could, however, be viewed by browsers running on the local server machine.

    Details: To enable the details of this specific error message to be viewable on remote machines, please create a tag within a "web.config" configuration file located in the root directory of the current web application. This tag should then have its "mode" attribute set to "Off".

<!-- Web.Config Configuration File -->

<configuration> <system.web> <customErrors mode="Off"/> 
     </system.web> </configuration>

    Notes: The current error page you are seeing can be replaced by a custom error page by modifying the "defaultRedirect" attribute of the application's configuration tag to point to a custom error page URL.

<!-- Web.Config Configuration File -->

<configuration> <system.web> <customErrors mode="RemoteOnly"  
    defaultRedirect="mycustompage.htm"/> </system.web> </configuration>

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Regarding BlogEngine 2.8, IIS 7.5 says:

64:   </system.serviceModel>
65:   <system.web.extensions>
66:     <scripting>

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...and regarding Umbraco 6:

164:   <!-- ASPNETAJAX -->
165:   <system.web.extensions>
166:     <scripting>

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So in both cases, the error is in the web.config file, and it is called "HTTP-error 500.19 - Internal Server Error". The error code is 0x80070032.
I can also say that it is the same online host, just another domain and hotel. It amazes me that I upload an unedited downloaded project that is successful build on my own computer (through VWD), but when it is uploaded - it's another story!
What's wrong, and how can i fix it?

Thanks in advance!
DanishCoder