Error in setup project HRESULT = '80004005'

I have a setup project which has been working fine for months. However, it has suddenly st开发者_C百科arted refusing to build with the error:

HRESULT = '80004005'

The setup project contains the output from three projects, and I have narrowed down the issue to one of them.

I have found a few questions here with this same issue and have tried them all, namely:

• Removed projects and re-added to the solution
• Removed all references and re-added

If I right click the project output in the setup project and select 'View Dependencies' the list is empty which seems to be a symptom others have found with this issue. However, despite several hours of googling, I have not managed to resolve it.

Ok - I finally found the answer. I checked each project file in my solution and found that on of them started with the line

<Project ToolsVersion="4.0"

where all the rest started:

<Project ToolsVersion="3.5"

I may have opened the project recently in VS2010 however the strange thing is it has worked fine since then. Anyway, changing the 4.0 to 3.5 solved it.

This may help:

• An error occurred while validating. HRESULT = '80004005'