Disk quota on webshares are active.
For most of those webshares, the disk quota is 5GB. Check in advance what your quota is (via DICT Selfservice) and how much disk space you are using today (in your explorer) and clean up if necessary.
Nothing can be written to the shares that are above their quota, not via explorer but also not from a web application.
Please do not keep backups or old versions of your websites on the webshare, even outside the WWW folder. The webshare is intended only for the files needed to make the production website work.
Are you currently using more disk space and cannot clean up (immediately)? Contact ICT HelpMe, if necessary we'll provide you with an alternative location for your data.