Recalled: File Manager stopped working

Without any apparent reason File Manager stopped working and throws the error below. It is followed by the regular back-end screen, I am not thrown out of the back-end. I noticed the error after uploading a folder with FTP, removing that folder did not make a difference. To my knowledge I have not changed anything recently, expect for an upgrade of the Memberlist extension. File synchronization turns into a disaster as it removed folders (not physically) and as a result pictures are not longer showing.

I am running a test site in the same hosting environment, this one does not have the error. The check tool reports no errors; I am running Contao 3.0.6.

Any help is appreciated.

Warning: scandir(/home/myuserid/domains/mydomain.com/public_html/tl_files/) [function.scandir]: failed to open dir: No such file or directory in system/helper/functions.php on line 183
#0 [internal function]: __error(2, 'scandir(/home/e...', '/home/myuserid/...', 183, Array)
#1 system/helper/functions.php(183): scandir('/home/myuserid/...')
#2 system/modules/core/drivers/DC_Folder.php(2592): scan('/home/myuserid/...')
#3 system/modules/core/drivers/DC_Folder.php(278): Contao\DC_Folder->generateTree('/home/myuserid/...', 0, false, false, Array)
#4 system/modules/core/classes/Backend.php(384): Contao\DC_Folder->showAll()
#5 contao/main.php(121): Contao\Backend->getBackendModule('files')
#6 contao/main.php(319): Main->run()
#7 {main}

Warning: scandir() [function.scandir]: (errno 2): No such file or directory in system/helper/functions.php on line 183
#0 [internal function]: __error(2, 'scandir() [generateTree('/home/myuserid/...', 0, false, false, Array)
#4 system/modules/core/classes/Backend.php(384): Contao\DC_Folder->showAll()
#5 contao/main.php(121): Contao\Backend->getBackendModule('files')
#6 contao/main.php(319): Main->run()
#7 {main}

Warning: Invalid argument supplied for foreach() in system/helper/functions.php on line 183
#0 system/helper/functions.php(183): __error(2, 'Invalid argumen...', '/home/myuserid/...', 183, Array)
#1 system/modules/core/drivers/DC_Folder.php(2592): scan('/home/myuserid/...')
#2 system/modules/core/drivers/DC_Folder.php(278): Contao\DC_Folder->generateTree('/home/myuserid/...', 0, false, false, Array)
#3 system/modules/core/classes/Backend.php(384): Contao\DC_Folder->showAll()
#4 contao/main.php(121): Contao\Backend->getBackendModule('files')
#5 contao/main.php(319): Main->run()
#6 {main}

Warning: Cannot modify header information - headers already sent by (output started at /home/myuserid/domains/mydomain.com/public_html/system/helper/functions.php:69) in system/modules/core/library/Contao/Template.php on line 277
#0 [internal function]: __error(2, 'Cannot modify h...', '/home/myuserid/...', 277, Array)
#1 system/modules/core/library/Contao/Template.php(277): header('Vary: User-Agen...', false)
#2 system/modules/core/classes/BackendTemplate.php(156): Contao\Template->output()
#3 contao/main.php(310): Contao\BackendTemplate->output()
#4 contao/main.php(125): Main->output()
#5 contao/main.php(319): Main->run()
#6 {main}

Warning: Cannot modify header information - headers already sent by (output started at /home/myuserid/domains/mydomain.com/public_html/system/helper/functions.php:69) in system/modules/core/library/Contao/Template.php on line 278
#0 [internal function]: __error(2, 'Cannot modify h...', '/home/myuserid/...', 278, Array)
#1 system/modules/core/library/Contao/Template.php(278): header('Content-Type: t...')
#2 system/modules/core/classes/BackendTemplate.php(156): Contao\Template->output()
#3 contao/main.php(310): Contao\BackendTemplate->output()
#4 contao/main.php(125): Main->output()
#5 contao/main.php(319): Main->run()
#6 {main}