Can't erase nRF51 flash?

[Elias]

I need to save data to flash on an nRF51422. I already have same basic thing working on an nRF52, so I figured the same API calls would work, but they don't. My main symptom is that sd_flash_page_erase() always returns NRF_ERROR_FORBIDDEN no matter what page I try to write to on the nRF51. I see this difference even if I try to erase flash first thing in main() on both chips. The function works as expected in the 52, but not the 51.

Is there some default difference in write access between the chips?

I'm using the s130 softdevice on the nRF51 and the s132 on the nRF52.

[Petter Myhre]

The nRF51 has a page size of 1kB.

With S130 v2 pages 0-108 will be protected, and sd_flash_page_erase() will return NRF_ERROR_FORBIDDEN.

The nRF52 has a page size of 4kB.

With S132 v2 pages 0-27 will be protected, and sd_flash_page_erase() will return NRF_ERROR_FORBIDDEN.