Getting error when trying to format date

JagannathaSutaDas 

The error is pretty specific: it's saying it cannot automatically parse your value for $InstalledOn - which is a [string] - into a [datetime] object (which is what the -Start parameter expects to receive.)

You don't show how you're populating $InstalledOn but I suppose that doesn't really matter.

You might find this error is due to a different in regional settings. For example, the date you're retrieving is in US format (month, day, year) but perhaps the script is running on a system configured  for something a different region that uses the "day, month, year" format.

You can try that yourself. If this generates the same error:

[datetime]::Parse("05/16/2022 08:42:38")

But the following works, then it's a difference in region.

[datetime]::Parse("16/05/2022 08:42:38")

Example output from both the above commands.

Still, once you've resolved this issue with $InstalledOn (there's multiple ways to resolve this), you're just going to run into another error since the assignment to $System on line one makes no sense when you look at how it's being used on line 2.

Here's one possible workaround for your issues. As I said above, I don't know how $InstalledOn is being populated so I'm simply assigning the text value from your error to it.

$InstalledOn = [datetime]::ParseExact("05/16/2022 08:42:38", "MM/dd/yyyy h:mm:ss", $null);
$System = Get-Date;
$DaySpan = New-TimeSpan -Start $InstalledOn -End $System;
$DaySpanDays = $DaySpan.Days;
$DaySpanDays;

Which produces the following output.

Cheers,

Lain

Edited to correct a typo.