Event-related brain potentials (ERPs) were recorded while participants read and made acceptability judgments about sentences containing three types of adjective sequences: (1) normal sequences--e.g., Jennifer rode a huge gray elephant; (2) reversed sequences that violate grammatical-semantic constraints on linear order--e.g., *Jennifer rode a gray huge elephant; and (3) contradictory sequences that violate lexical-semantic constraints on compositionality--e.g., *Jennifer rode a small huge elephant. Relative to the control condition, the second adjective elicited a reduced N400 and an enhanced P600 in both the reversal condition and the contradiction condition. We present several alternative accounts of these two effects, but favor an interpretation which treats them as reflecting semantic and syntactic aspects of a temporary reanalysis of the adjective order construction. Furthermore, relative to the control condition, the final noun elicited a robust N400 in the contradiction condition but not in the reversal condition. We suggest that this effect indexes the full registration of the lexical-semantic incompatibility of the two adjectives in the contradiction condition. Finally, we discuss how all of these findings fit into the broader context of recent ERP studies that have reported atypical N400s and robust P600s in response to certain types of semantic anomalies.