Hi Apoorv,
Reason for this error is when you try to execute the program /SAPSLL/PREF_AGREEMNTS_SYNC_R3 in ECC it try to read some data from associated GTS system. Authorization object GTS_PRE is checked with activity 03 for the RFC user used for this communication. Please switch on trace in GTS system and you will find missing auth object there.
Assign authorization for auth object GTS_PRE to RFC user used for communication in GTS system. This will fix the issue.
Let me know if this helps to fix the issue.
BR,
Chetan