Ensure your card is formatted as FAT32 with 32KB or 64KB clusters. The Hacks Guide provides detailed formatting instructions.
: Although often associated with a different code, a lack of "blocks" can occasionally trigger generic installation failures. failed to install cia file 0xd8e0806a
If you are attempting to install the application itself and getting this error, your system is not yet modded. You cannot install a CIA file (including FBI) on a stock, unmodded 3DS. Ensure your card is formatted as FAT32 with
If your CFW is up to date and SigPatches are applied, the issue might be the file itself. failed to install cia file 0xd8e0806a