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what exactly did you change in the windows installation that is working ok now? is it easy to implement on all Filerun users' computers?

mbstring is active on this server:

You are right, there is no error of that type on the demo server.

I also get this mysql error - SQLSTATE[HY000]: General error: 1267 Illegal mix of collations (utf8mb4_unicode_ci,IMPLICIT) and (cp1251_general_ci,COERCIBLE) for operation '='

I figured it out - it's the capital letters - if there are more than 5 capital letters in the file name - the missing id appears, if less, the file becomes viewable. Weird!

I think it's something to do with the file names. I changed the names and the files become viewable. 

I changed the file viewer to Zoho, but it was reporting a similar error, so it is not from the viewer plugin.

But I can not really figure out what exactly in the name breaks the code. Any special characters like dashes, dots, capital letters?

I need to add that the files are loaded from a base folder which is CHMOD 755, I have uploaded them via ftp. May be change the CHMOD?

Hi, in the access log I can see a track of my actions with my IP, but also an IP of Microsoft acessing - 52.149.105.46. I did try to open the 3 documents again and a second document is missing weblink id now. Is it possible that Microsoft is breaking the links?