This article explains the microSD Card requirements for I-Series 1.0 Offline OTA Upgrade

I-Series devices can use microSD cards for performing offline OTA updates if needed. For the cards to be readable, they must not exceed the following specifications:

1. microSD card must be Class 4 rated
2. microSD card must not exceed 16 GB in size
3. microSD card must be formatted in FAT32

Newer cards - or cards that exceed these specifications - may experience unexpected results including, but not limited to, unreadable data.