Error: Reqiest failed - The file exists

Getting the following debug/error when attempting to Request Certificate.
While I’ve checked all permissions on all the relevant folders I could think of, the issue persists.

2018-06-07 13:19:51.547 +10:00 [INF] Beginning Certificate Request Process: Maximizer
2018-06-07 13:19:51.552 +10:00 [INF] Registering Domain Identifiers
2018-06-07 13:19:51.552 +10:00 [INF] Attempting Domain Validation: FQDN
2018-06-07 13:19:51.552 +10:00 [INF] Registering and Validating FQDN 
2018-06-07 13:19:54.774 +10:00 [INF] Domain already has current authorization, skipping verification: FQDN
2018-06-07 13:19:54.774 +10:00 [INF] Requesting Certificate via Lets Encrypt
2018-06-07 13:20:06.650 +10:00 [INF] Maximizer: Request failed - The file exists.
 System.IO.IOException: The file exists.

   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.__Error.WinIOError()
   at System.IO.Path.InternalGetTempFileName(Boolean checkHost)
   at Certify.ACMESharpCompat.ACMESharpUtils.UpdateCertificate(String certificateRef, String PkiTool, String vaultProfile) in D:\Work\GIT\certify\src\Certify.Core\ACMESharpCompat\ACMESharpUtils.cs:line 865
   at Certify.VaultManager.PerformCertificateRequestProcess(String domainIdentifierRef, String[] alternativeIdentifierRefs) in D:\Work\GIT\certify\src\Certify.Core\Management\VaultManager.cs:line 1194
   at Certify.Management.APIProviders.ACMESharpProvider.PerformCertificateRequestProcess(String primaryDnsIdentifier, String[] alternativeDnsIdentifiers) in D:\Work\GIT\certify\src\Certify.Core\Management\APIProviders\ACMESharpProvider.cs:line 139
   at Certify.Management.CertifyManager.<PerformCertificateRequestProcessing>d__52.MoveNext() in D:\Work\GIT\certify\src\Certify.Core\Management\CertifyManager.cs:line 682
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd(Task task)
   at Certify.Management.CertifyManager.<PerformCertificateRequest>d__51.MoveNext() in D:\Work\GIT\certify\src\Certify.Core\Management\CertifyManager.cs:line 420
2018-06-07 13:20:06.650 +10:00 [INF] Maximizer: Request failed - The file exists.
 System.IO.IOException: The file exists.

Implication from calls looks like suggestion of Temp files/folder?

ed: site detail replaced with FQDN

ed2: I guess I answered my own question (I know how often that happens for the people we help) - used procmon and found Certify having trouble with files in c:\windows\temp. Purged folder and fixed permissions, next request worked successfully. Not the first Windows install where the temp folder permissions have been mucked up by something.

Hi Paul, yes the temp folder does play a part for some operations. Windows has a limit of 65535 temp files under the current temp path, so it’s common that it fills up then strange errors start to appear.