Follow these steps:
Navigate to C:\inetpub\wwroot\wss\Virtual Directories\your web app's virtual directory
here.
- You can also open IIS
- Expand Sites
- Right click on your SharePoint site
- Choose explore
- proceed to step 2
Copy and paste the web.config file (making a backup)
- Open web.config using notepad
- Search for “CallStack” , set this equal to true
- Search for “Custom”, set the
customerrors = “Off”
- Search for “Debug”, set Debug = “True”
- Save the web.config file and refresh your page in the browser
You should now see what the error actually is.
Many times it is a web part assembly reference missing from the web.config , custom master page missing or something similar.
This should at least give you a more precise troubleshooting starting point. Remember to turn CustomErrors back “On” in the web.config after fixing the issue so that your end users won’t see an ugly Asp.Net error if this happens again.