Error on webpage access. The other services (files sync, contacto sync,etc) work

I have a problem with web access.
I receive en error (The server is not able to complete request…Remote address: xxx.xxx.xxx.xxx - Request ID xxxxxxxxxxx
The other services are working.
What can I do?
Thank you in advance.
Sergio

The nextcloud log says:
{“reqId”:“EPeKf5KGtbtcWU1LevUR”,“level”:3,“time”:“2019-05-08T19:54:38+00:00”,“remoteAddr”:“192.168.2.100”,“user”:“sergio”,“app”:“PHP”,“method”:“GET”,“url”:"/index.php/apps/files/",“message”:“touch(): Unable to create file /data/nextcloud/appdata_ocvn587klisk/css/icons/icons-list.template because Input/output error at /var/www/nextcloud.15.0.7b/lib/private/Files/Storage/Local.php#206”,“userAgent”:“Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0”,“version”:“15.0.7.0”}
{“reqId”:“EPeKf5KGtbtcWU1LevUR”,“level”:3,“time”:“2019-05-08T19:54:38+00:00”,“remoteAddr”:“192.168.2.100”,“user”:“sergio”,“app”:“PHP”,“method”:“GET”,“url”:"/index.php/apps/files/",“message”:“touch(): Unable to create file /data/nextcloud/appdata_ocvn587klisk/css/icons/icons-vars.css because Input/output error at /var/www/nextcloud.15.0.7b/lib/private/Files/Storage/Local.php#206”,“userAgent”:“Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0”,“version”:“15.0.7.0”}
{“reqId”:“EPeKf5KGtbtcWU1LevUR”,“level”:3,“time”:“2019-05-08T19:54:38+00:00”,“remoteAddr”:“192.168.2.100”,“user”:“sergio”,“app”:“PHP”,“method”:“GET”,“url”:"/index.php/apps/files/",“message”:“stat(): stat failed for /data/nextcloud/appdata_ocvn587klisk/css/icons/icons-vars.css at /var/www/nextcloud.15.0.7b/lib/private/Files/Storage/Local.php#142”,“userAgent”:“Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0”,“version”:“15.0.7.0”}
{“reqId”:“EPeKf5KGtbtcWU1LevUR”,“level”:3,“time”:“2019-05-08T19:54:38+00:00”,“remoteAddr”:“192.168.2.100”,“user”:“sergio”,“app”:“index”,“method”:“GET”,“url”:"/index.php/apps/files/",“message”:{“Exception”:“OCP\Files\NotFoundException”,“Message”:“File does not exist”,“Code”:0,“Trace”:[{“file”:"/var/www/nextcloud.15.0.7b/lib/private/Files/SimpleFS/SimpleFile.php",“line”:108,“function”:“checkFile”,“class”:“OC\Files\SimpleFS\SimpleFile”,“type”:"->",“args”:[]},{“file”:"/var/www/nextcloud.15.0.7b/lib/private/Template/IconsCacher.php",“line”:137,“function”:“putContent”,“class”:“OC\Files\SimpleFS\SimpleFile”,“type”:"->",“args”:[":root {\n–icon-confirm-fade-000: url(data:image/sv example

[/details]

Nextcloud version (15.0.7):
Operating system and version (Ubuntu 16.04):
Apache (Apache 2.4.18)_:
PHP version (7.0.33):

I try to reinstall nextcloud (only files) but no success

My config.php

<?php $CONFIG = array ( 'instanceid' => 'instanceid', 'passwordsalt' => 'password', 'secret' => 'secret string', 'trusted_domains' => array ( 0 => 'xxxxxxxx', 1 => 'xxxxxx', 2 => 'xxxxxx', 3 => 'xxxxxxxx', ), 'datadirectory' => '/data/nextcloud', 'overwrite.cli.url' => 'http://xxxx.xxxx.xxxx', 'dbtype' => 'mysql', 'version' => '15.0.7.0', 'dbname' => 'nextcloud', 'dbhost' => 'localhost', 'dbtableprefix' => 'oc_', 'dbuser' => 'dbuser', 'dbpassword' => 'DBpassword', 'logtimezone' => 'UTC', 'installed' => true, 'mail_smtpmode' => 'smtp', 'mail_smtpsecure' => 'ssl', 'mail_from_address' => 'xxx.xxxx', 'mail_domain' => 'xxx.xx', 'mail_smtpauth' => 1, 'mail_smtphost' => 'smtp.xxx.xxx', 'mail_smtpport' => 'xxx', 'mail_smtpname' => 'email@email.com', 'mail_smtppassword' => 'password', 'mail_smtpauthtype' => 'PLAIN', 'redis' => array ( 'host' => '127.0.0.1', 'port' => 6379, ), 'memcache.locking' => '\\OC\\Memcache\\Redis', 'updater.release.channel' => 'production', 'maintenance' => false, 'loglevel' => 2, 'theme' => '', 'memcache.local' => '\\OC\\Memcache\\Redis', 'auth.bruteforce.protection.enabled' => true, 'trashbin_retention_obligation' => 'auto', 'versions_retention_obligation' => 'auto', 'twofactor_enforced' => 'false', 'twofactor_enforced_groups' => array ( ), 'twofactor_enforced_excluded_groups' => array ( ), 'updater.secret' => 'xxxxxxxxxxxxxxxx', );