Basically there are two possible solutions:
1) system environment variable -> SAPLOGON_INI_FILE
http://forums.sdn.sap.com/thread.jspa?threadID=1465508
2) corrupted saplogon.ini -> Note 1219265
Basically there are two possible solutions:
1) system environment variable -> SAPLOGON_INI_FILE
http://forums.sdn.sap.com/thread.jspa?threadID=1465508
2) corrupted saplogon.ini -> Note 1219265