To reproduce this, build Qt using the following steps:

Open the x64 command prompt from the VS2010 tools menu
set the QTDIR and PATH
configure -platform win32-msvc2010 <other options>
nmake

In the x64 command prompt, browse to an existing Qt project with a .pro file
qmake -tp vc
devenv <name of project>.vcprojx /useenv

Attempt to build the project. The following error (or similar) is seen in the output window:

TRACKER : error TRK0002: Failed to execute command: ""c:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\BIN\amd64\link.exe" /ERRORREPORT:PROMPT @C:\Users\Administrator\AppData\Local\Temp\2a5d48726d294cba995748a177f15b3d.rsp". The operation identifier is not valid.

The project can be built from the command line without issue, using qmake / nmake

A suggested workaround which has been verified by at least one person is to change the active configuration from win32 to x64 (copying the settings from win32) in the configuration manager of the VS2010 IDE. Alternatively, the project can be built from the command line.

The problem seems to be that qmake does not generate the project file correctly so that the active configuration is set to x64. This results in the wrong path being chosen for link.exe (the x86 version instead of the x64 version).