TMockRunner NUnitLaucher dotcover?

I have this script which runs out tests through TypeMock:

$source="%system.teamcity.build.workingDir%\Tests\**\bin\*.Tests.dll"
$tmockrunner="C:\Program Files (x86)\Typemock\Isolator\7.1\TMockRunner.exe"
$nunitlauncher="%system.teamcity.dotnet.nunitlauncher%"

$bin = Get-ChildItem $source
foreach ($item in $bin) {
    &$tmockrunner -target 4.0 "$nunitlauncher" v4.0 x64 NUnit-2.6.2 $item.FullName
}

I want to include dotcover coverage, but this script returns the following exception:

$source="%system.teamcity.build.workingDir%\Tests\**\bin\*.Tests.dll"
$tmockrunner="C:\Program Files (x86)\Typemock\Isolator\7.1\TMockRunner.exe"
$nunitlauncher="%system.teamcity.dotnet.nunitlauncher%"
$dotcover="%teamcity.dotCover.home%"

$bin = Get-ChildItem $source
foreach ($item in $bin) {
    &$tmockrunner -target 4.0 "$nunitlauncher" v4.0 x64 NUnit-2.6.2 $item.FullName /dotcover:"$dotcover"
}

"Coverage output is not specified.
Type 'dotCover help' for usage."

How can I get dotcover working?