The default ScriptType for Windows guest OS is PowerShell.
So you probably have an error saying that there is an "unexpected token" or something along that line.
You will have to make sure that PowerShell sees that first part as a [string], so place it between quotes.
Something like this
$guestvms="flash3"
$myscript='"e:\testfile.dat 8 0x0 11000" | Out-File C:\SQLIO\param.txt'
Invoke-VMScript-VM$guestvms-ScriptText$myscript-GuestUseradministrator-GuestPasswordPassword
Those are single quotes on the outside double quotes around the [string].