Stuck at setting Manager field in AD by pulling the attribute from Oracle HRMS database.

Hi,
I need help in AD powershell command wherein I am pulling Employee manager from HRMS Oracle database & setting it on AD user account.

Let me segment all question into small small parts.

1) Using below string to connect to oracle HRMS database.

#connect to Oracle  
#creating password secure string 
     $oracleconstr = "User Id=UserA;Password=pass@123;Data Source=192.168.10.121/HR"
    $oracleconn= New-Object Oracle.DataAccess.Client.OracleConnection($oracleconstr)
    $oracleconn.Open()



2) Fetching Employee Manager name from Oracle table & saving it in variable $ManagerIDDB

    $oracle = "Select Manager from SYSADM.ACTIVE_EMPLOYEE where EMPLID = '($user.Employeeid)'"
    $oraclecommand = New-Object Oracle.DataAccess.Client.OracleCommand($oracle,$oracleconn)   
    $ManagerIDDB=$oraclecommand.ExecuteScalar()



3) I am using for loop for all AD users by putting some condition like comparing manager attribute from HRMS Oracle & AD which i uses for setting correct Manager in AD.

$userlist = Get-ADUser -Filter * -SearchBase "OU=BU,DC=ABC,DC=com" -Properties * | where {$_.Enabled -eq $TRUE}
foreach($user in $userlist)
{

$managerDB = Get-Aduser -filter {EmployeeID -eq $ManagerIDDB}

Set-Aduser $user -Manager $managerDB

But this gives error as below in setting up Manager.

====================================================

Set-ADUser : Cannot convert 'System.Object[]' to the type 'Microsoft.ActiveDire
ctory.Management.ADUser' required by parameter 'Manager'. Specified method is n
ot supported
====================================================


Please help guys.