Have you checked logs in Event Viewer?

Where should i find it?

i looked at Event viewer and it mentioned something about w3wp.exe not working correctly, what is the problem with it?

Without seeing the event description, I really couldn’t guess. If you post that, I will do my best to guess 

Ok here it is : 

Well, despite the fact that I can't read what I can only assume to be German, I would guess the password saved in web.config to connect to the database is wrong.

the error always is on asp.Net 4.0 w3wp.exe with message:

The type “System.Attribute” is defined in an assembly that is not referenced, You must add a reference for “netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51”

The error in Event Viewer appears to be a SQL exception during connection.

Are you getting another error somewhere else?

Hi Hamzamara,

The message is in French and it seems to indicate an error in the db login from the site (in IIS) to the database.

Try this please:

1. Go to IIS,
2. Click on the name of the site for the Acumatica instance,
3. On the right side of the panel, double click on Connection Strings,
4. Check the credentials for ProjectX: make sure that the logon to the database is successful with those credentials.