I found this in log file:
[exception] [e66a958595cd23350b3269c9] /plavorexitbeta/api.php Flow\Exception\InvalidDataException from line 253 of C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Collection\AbstractCollection.php: Invalid workflow: ugvzzs70cj48wj9t
#0 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Collection\AbstractCollection.php(238): Flow\Collection\AbstractCollection->getWorkflow()
#1 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Model\AbstractRevision.php(413): Flow\Collection\AbstractCollection->getTitle()
#2 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Data\Listener\ReferenceRecorder.php(249): Flow\Model\AbstractRevision->getContent(string)
#3 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Data\Listener\ReferenceRecorder.php(115): Flow\Data\Listener\ReferenceRecorder->getReferencesFromRevisionContent(Flow\Model\Workflow, Flow\Model\PostRevision, Flow\Model\PostRevision)
#4 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Data\Listener\ReferenceRecorder.php(82): Flow\Data\Listener\ReferenceRecorder->calculateChangesFromExisting(Flow\Model\Workflow, Flow\Model\PostRevision)
#5 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Data\ObjectManager.php(264): Flow\Data\Listener\ReferenceRecorder->onAfterInsert(Flow\Model\PostRevision, array, array)
#6 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Data\ObjectManager.php(173): Flow\Data\ObjectManager->insert(array, array)
#7 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Data\ObjectManager.php(146): Flow\Data\ObjectManager->multiPut(array, array)
#8 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Data\ManagerGroup.php(80): Flow\Data\ObjectManager->put(Flow\Model\PostRevision, array)
#9 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Block\TopicListBlock.php(178): Flow\Data\ManagerGroup->put(Flow\Model\PostRevision, array)
#10 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\SubmissionHandler.php(150): Flow\Block\TopicListBlock->commit()
#11 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\WorkflowLoader.php(66): Flow\SubmissionHandler->commit(Flow\Model\Workflow, array)
#12 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Api\ApiFlowBasePost.php(35): Flow\WorkflowLoader->commit(array)
#13 C:\inetpub\wwwroot\plavorexitbeta\extensions\Flow\includes\Api\ApiFlow.php(98): Flow\Api\ApiFlowBasePost->execute()
#14 C:\inetpub\wwwroot\plavorexitbeta\includes\api\ApiMain.php(1584): Flow\Api\ApiFlow->execute()
#15 C:\inetpub\wwwroot\plavorexitbeta\includes\api\ApiMain.php(535): ApiMain->executeAction()
#16 C:\inetpub\wwwroot\plavorexitbeta\includes\api\ApiMain.php(506): ApiMain->executeActionWithErrorHandling()
#17 C:\inetpub\wwwroot\plavorexitbeta\api.php(83): ApiMain->execute()
#18 {main}
ApiMain::setCacheMode: setting cache mode private
[Mime] MimeAnalyzer::loadFiles: loading mime types from C:\inetpub\wwwroot\plavorexitbeta\includes/libs/mime/mime.types
[Mime] MimeAnalyzer::loadFiles: loading mime info from C:\inetpub\wwwroot\plavorexitbeta\includes/libs/mime/mime.info
[error] [e66a958595cd23350b3269c9] /plavorexitbeta/api.php ErrorException from line 100 of C:\inetpub\wwwroot\plavorexitbeta\includes\libs\HttpStatus.php: PHP Warning: Unknown HTTP status code invalid-workflow
#0 [internal function]: MWExceptionHandler::handleError(integer, string, string, integer, array)
#1 C:\inetpub\wwwroot\plavorexitbeta\includes\libs\HttpStatus.php(100): trigger_error(string, integer)
#2 C:\inetpub\wwwroot\plavorexitbeta\includes\WebResponse.php(106): HttpStatus::header(string)
#3 C:\inetpub\wwwroot\plavorexitbeta\includes\api\ApiFormatBase.php(181): WebResponse->statusHeader(string)
#4 C:\inetpub\wwwroot\plavorexitbeta\includes\api\ApiMain.php(1808): ApiFormatBase->setHttpStatus(string)
#5 C:\inetpub\wwwroot\plavorexitbeta\includes\api\ApiMain.php(600): ApiMain->printResult(string)
#6 C:\inetpub\wwwroot\plavorexitbeta\includes\api\ApiMain.php(544): ApiMain->handleException(Flow\Exception\InvalidDataException)
#7 C:\inetpub\wwwroot\plavorexitbeta\includes\api\ApiMain.php(506): ApiMain->executeActionWithErrorHandling()
#8 C:\inetpub\wwwroot\plavorexitbeta\api.php(83): ApiMain->execute()
#9 {main}
MediaWiki::preOutputCommit: primary transaction round committed
MediaWiki::preOutputCommit: pre-send deferred updates completed
MediaWiki::preOutputCommit: LBFactory shutdown completed
[cookie] ''(Hidden)''
[cookie] ''(Hidden)''
Request ended normally
[session] Saving all sessions on shutdown
[DBConnection] Wikimedia\Rdbms\{closure}: closing connection to database ''.