Secret of "Guitar Star" Challenge Unlokced!
From
http://sims.wikia.com/wiki/Guitar_skill#Challenges
Guitar Star
Guitar Stars must play at 10 Parties and Venues in the town to earn their title. Afterwards, they earn larger monetary rewards for tips and performances!
* This may be one of the hardest challenge to complete. The description is very misleading. You can not be Guitar Star just by having 10 house parties with friends and play guitar there. You must succeed in 10 guitar skill opportunity card. It is not Music career opportunity card. The hardest part is getting the guitar skill opportunity card at all. It is recommended you don't have any job (including Music career) and any other skill (not even basic cooking skill. Eat Quick Meal or Pizza). Just play guitar for tip on the park and street day and night, day after days. Then, the opportunity cards will come. It takes about 6 sim weeks.