Writing to FLASH on MSP430F5529
To erase and write to the Information memory, you have to clear the LOCKINFO bit in the FCTL4 register. This bit is usually cleared on reset already, but it doesn't hurt to check.

But information memory A is different (and 0x1980 is in that range). It has another lock bit LOCKA in FCTL3. This is set on reset and prevents erasing and writing to information memory A.

To clear that bit you have to write a 1 to it (counter intuitive).

I would suggest you use a different information memory location, as information memory A holds some calibration values from TI which you probably don't want to erase (if my memory serves me right, it's been a few years).