Hi, the problem is, this is in fact not related to Phoca Gallery, but to Joomla! or server settings. Phoca Gallery does not install itself. You install Phoca Gallery in Joomla! and this message comes from extension manager of Joomla! which cannot upload this file to the server.
Mostly this can be due to limits on server. Try to check upload limits on your server (uploading files and POST sizes - as upload belongs to POST). If you have some server hosting provider, just try to ask him.
Not sure, if enabling debug mode will help but try to enable debug mode, maybe you get more detailed message when you upload the version 4.3.0 on your server
The same with errorLog and php errors, try to enable them, try to see your errorLog on your server, maybe there will be error message which says more.
(
https://www.phoca.cz/documents/16-joomla ... rs-on-site )
As written above, if fact this is something which is not related to Phoca Gallery as it wasn't even installed on the system so no problem of Phoca Gallery cannot be solved or discussed here as it was even not installed on your server. The problem is with uploading file on your server (maybe it is because it is too large and there are limits on the server, etc.)
So first try to see all the debug information, errorLogs, etc., try to ask webhosting provider.
Jan