Hi Grégory Nallet you can see in the Server reference manual all about .meta files as this:
9.1 User Documents
A user document is the document that an end user sees when accessing a document on QlikView Server (QVS). To fully identify a user document, both the QVS server/cluster and the path relative to the server have to be known. Technically, a user document consists of three files:
1. .qvw file that contains the data and layout.
2. .META file that contains:
a. AccessPoint attributes
b. Pre-load options
c. Authorization (Document Metadata Service – that is, DMS – mode only)
3. .Shared file (see below)
Note! If the user document is distributed by the QlikView Distribution Service, both the .qvw and the data in the .META file are overwritten.
-There are multiple objects available for user collaboration and sharing through QlikView Server:
-Sheet objects, including charts
From Server Reference Manual pp. 51 (Attached)
And concerning to the "Unexpected Error Occurred" have you been able to reproduce the issue, and are you totally sure by deleting the .meta files you solve the problem?