The title gives a hint that this is a Caesar and Transposition cipher combined:
"THISWASACAESARSHIFTOFSEVENTEENFOLLOWEDBYATRANSPOSITIONOFROWSANDCOLUMN\
STHISOFCOURSERETAINSTHELETTERFREQUENCIESOFENGLISHWHICHPROBABLYHELPEDYO\
UDECIPHERTHISINTHISCASETHETWOMETHODSOFENCRYPTIONCOMMUTEHOWEVERTHISISNT\
ALWAYSTHECASEAPARTFROMSOMESPECIALCASESIFWEUSEAVIGENERECIPHERANDTHENATR\
ANSPOSITIONWEWILLGETADIFFERENTRESULTDEPENDINGONWHICHORDERWEDOTHEMINCAN\
YOUFINDANYCASESWHERETHEYWILLCOMMUTE"
I solved this by running it through my Vigenere cipher solver (I didn't bother to write a separate Caesar solver), which yielded the key RR - this was enough of a pointer to me that it was a Caesar shift of R. Then I did the transposing trick of the previous cipher, Mathematica code:
Partition[Characters[str], 16] // Transpose // StringJoin