WP Lets Encrypt in IIS not possible

Hi
I try to install WP lets Encrypt on my WordPress Websites on IIS. The following fatal error happens:

ERROR: CREATE_CLIENT:RuntimeException: Could not generate key pair! Check your OpenSSL configuration. OpenSSL Error:
error:02001003:system library:fopen:No such process
error:2006D080:BIO routines:BIO_new_file:no such file
error:0E064002:configuration file routines:CONF_load:system lib
error:02001003:system library:fopen:No such process
error:2006D080:BIO routines:BIO_new_file:no such file
error:0E064002:configuration file routines:CONF_load:system lib
in C:\inetpub\KSSPartners_WP\wp-content\plugins\wp-letsencrypt-ssl\lib\LEFunctions.php:65
Stack trace:
#0 C:\inetpub\KSSPartners_WP\wp-content\plugins\wp-letsencrypt-ssl\lib\LEAccount.php(72): WPLEClient\WPLEFunctions::RSAGenerateKeys(NULL, ‘C:\\inetpub\\KSSP…’, ‘C:\\inetpub\\KSSP…’)
#1 C:\inetpub\KSSPartners_WP\wp-content\plugins\wp-letsencrypt-ssl\lib\LEClient.php(141): WPLEClient\LEAccount->__construct(Object(WPLEClient\WPLEConnector), 1, ‘[email protected]’, Array)
#2 C:\inetpub\KSSPartners_WP\wp-content\plugins\wp-letsencrypt-ssl\classes\le-core.php(100): WPLEClient\WPLEClient->__construct(‘[email protected]’, false, 1, ‘C:\\inetpub\\KSSP…’)
#3 C:\inetpub\KSSPartners_WP\wp-content\plugins\wp-letsencrypt-ssl\classes\le-core.php(78): WPLE_Core->wple_create_client()
#4 C:\inetpub\KSSPartners_WP\wp-content\plugins\wp-letsencrypt-ssl\classes\le-core.php(63): WPLE_Core->wple_generate_verify_ssl()
#5 C:\inetpub\KSSPartners_WP\wp-content\plugins\wp-letsencrypt-ssl\admin\le_admin.php(352): WPLE_Core->__construct(Array)
#6 C:\inetpub\KSSPartners_WP\wp-includes\class-wp-hook.php(288): WPLE_Admin->wple_save_email_generate_certs(”)
#7 C:\inetpub\KSSPartners_WP\wp-includes\class-wp-hook.php(312): WP_Hook->apply_filters(NULL, Array)
#8 C:\inetpub\KSSPartners_WP\wp-includes\plugin.php(478): WP_Hook->do_action(Array)
#9 C:\inetpub\KSSPartners_WP\wp-admin\admin.php(170): do_action(‘admin_init’)
#10 {main}

What can i do?

Best regards from Switzerland and thanks for the support
Kurt