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.
If none of the above work, the CIA is likely – obtain a clean copy from a different source. failed to install cia file 0xd8e0806a
Your microSD card may be failing, improperly formatted (it should be FAT32), or have a corrupted file system. If you are attempting to install the application
Please reply with:
: A corrupt file system or a failing physical SD card can lead to data errors that cause verification to fail. improperly formatted (it should be FAT32)
: Although often associated with a different code, a lack of "blocks" can occasionally trigger generic installation failures.