Solution
The PXIe-5423 does indeed have 128MB of onboard memory, but the error you're encountering is due to a limitation in the number of sequences that can be stored in the device’s sequence memory (not the waveform memory).
Maximum number of sequences:
Internal trigger mode: 2047 sequences
External trigger mode: 1023 sequences
This means that attempting to register 32,000 sequences exceeds the sequence memory capacity, regardless of how small each waveform is.