by Ken Task.
This is really a question for ALL ... ;)
My 2 cents ...
"cannot connect to the server" ... is that on uploading or after the file uploads and begins the process of extracting the .mbz file?
How are you hosted? Shared systems do have caps/maxes as well as settings for size of file to upload in PHP settings - which then affect Moodle. Normally, the file too large error is trapped and the error reported tells you the file is too large.
The second ... when it begins the process of extracting ... the server that it might not be able to connect to is the DB server. OR the script times out - so settings in PHP for max time for a script to execute, etc. Those can be seen via Moodle Admin interface, Server, PHP Info link.
Also you might need to turn on debugging to see if that produces any specific info you could share back here.
'spirit of sharing', Ken