This may be due to the fact that you did not upgrade your in-game version of the low-level I/O hook. You need to get the new sample
(AkDefaultIOHookBlocking or AkDefaultIOHookDeferred) from $WWISESDK/samples/SoundEngine/$PLATFORM/ and replace or merge the changes in your own low-level I/O hook.
Before Wwise 2010.1, AkTransferInfo::uRequestedSize was actually representing the buffer size into which the low-level I/O hook was allowed to write. Now, it represents the exact number of bytes that has to be transferred, and the buffer size into which the low-level I/O hook is allowed to write is represented by AkTransferInfo::uBufferSize. Now, some file systems do not support reading sizes that are not multiple of a certain value. For example, on Windows, files opened with the FILE_FLAG_NO_BUFFERING flag need to be read in multiples of the sector size, even for the last bytes of the file. In such cases, you should try to read AkTransferInfo::uBufferSize instead of AkTransferInfo::uRequestedSize from the platform I/O API.
Typically, you specify read size constraints by returning the proper value from IAkLowLevelIOHook::GetBlockSize(). For example, the "deferred I/O hook" on Windows opens files with the FILE_FLAG_NO_BUFFERING flag, and returns 2048 (bytes) from IAkLowLevelIOHook::GetBlockSize(). AkTransferInfo::uBufferSize is always a multiple of this value.
