Hi, when database "limesurvey" in mssql is case sensitive (SQL_Latin1_General_CP1_CS_AS, for example), the function mssql_drop_coulmn_with_constraints in activate_helper.php doesn't work because the query is lowercase.
I had to correct it in the following way:

function mssql_drop_coulmn_with_constraints($tablename, $columnname)
{
Yii::app()->loadHelper("database");

// find out the constraint name of the old primary key
$pkquery = "SELECT CONSTRAINT_NAME
FROM INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE
WHERE TABLE_NAME = '" . $tablename . "' AND COLUMN_NAME = '" . $columnname . "'";

$result = Yii::app()->db->createCommand($pkquery)->queryAll();
foreach ($result as $constraintName) {
    Yii::app()->db->createCommand('alter table [' . $tablename . '] drop constraint "' . $constraintName['CONSTRAINT_NAME'] . '"')->execute();
}
$success = Yii::app()->db->createCommand('ALTER TABLE [' . $tablename . '] DROP COLUMN "' . $columnname . '"')->execute();
return $success;

}

please note the ortographic error in name, as already reported in 19110 , still unresolved.

Many thanks!