Trying to use a waitforexit Powershell Script

I have a step in a deployment that checks to see when something ends and then send a file to a folder with the machine name.  i have been able to do this when checking for other processes, but when i use a wildcard for the process name it fails. The problem is the process name is not consistent, it usually begins with a number string followed by .ftwlaunch.exe.  below is the script and the failure output, can someone please tell me what is wrong.

$a = get-process *.ftwlaunch.exe

$a.waitforexit()

Write-Output "DONE" | Out-File "\\wlsrvr-fs1\users\fidessa\finished\$env:computername.txt"

Exception setting "BufferSize": "Cannot set the buffer size because the size specified is too large or too small.
Parameter name: value
Actual value was 250,300."
At C:\WINDOWS\AdminArsenal\PDQDeployRunner\service-1\exec\Error Handling Wrapper.ps1:7 char:5
+ $rawUI.BufferSize = $newSize
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], ParentContainsErrorRecordException
+ FullyQualifiedErrorId : ExceptionWhenSetting