Powershell losing variables

Hi there,

sometimes variables are losing their values and I dont know why - e.g.:

$Comp = gwmi -query ("Select SystemType,DnsHostName,Domain,DomainRole from Win32_ComputerSystem")

If ($comp.DomainRole -match "3")
{
$SetUsername=$comp.domain+'\'+$UserName
$domain = New-Object DirectoryServices.DirectoryEntry
$search = [System.DirectoryServices.DirectorySearcher]$domain
$search.Filter = "(&(objectClass=Computer)(cn=$comp.dnshostname))"
$Computer = $search.FindOne().GetDirectoryEntry()
}

The variable $comp.dnshostname is not working at this position:

$search.Filter = "(&(objectClass=Computer)(cn=$comp.dnshostname))"


But if I put the variable into a new one it works - e.g.

$Comp = gwmi -query ("Select SystemType,DnsHostName,Domain,DomainRole from Win32_ComputerSystem")

If ($comp.DomainRole -match "3")
{
$SetUsername=$comp.domain+'\'+$UserName
$GetComp=$comp.dnshostname
$domain = New-Object DirectoryServices.DirectoryEntry
$search = [System.DirectoryServices.DirectorySearcher]$domain
$search.Filter = "(&(objectClass=Computer)(cn=$getcomp))"
$Computer = $search.FindOne().GetDirectoryEntry()
}

I put the variable $comp.dnshostname into a new one $GetComp:

$GetComp=$comp.dnshostname

Now it works at the above mentioned position:

$search.Filter = "(&(objectClass=Computer)(cn=$GetComp))"

Why can't I work with $comp.dnshostname directly?

Cheerio