Hi,
The HikaShop configuration form contains a lot of fields (a lot of data).
When you want to include a file in the form submission, some server have limitation/restriction and they does not like receiving so much data.
When you upload a file, the form is not submitted in the same format than without a file, it consumes more data.
It is planned to separate the upload part form the configuration (like I did for HikaMarket) but for the moment, you will have to upload the file manually and change the value in the database (or find a server without this limitation/restriction).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.