I moved the thread from the Technical Forum to Pharaoh Game Help.
jpy,
Please use an informative thread subject. For example, this might be called "Prosperity won't rise".
There are 2 main aspects to Prosperity: the "cap" and the rate of change. Rough cottages give a Prosperity "cap" of 25, so your problem is probably in the rate of change.
If a city makes money and isn't otherwise too bad (not too much unemployment, etc), then Prosperity typically rises a few each quarter-year until it hits the "cap". Losing money in a year, however, can cause a rapid fall in Prosperity.
Prosperity 0 typically indicates that the city lost money the previous year. I haven't played Maritis (or any other Cleopatra mission), but it appears to be able to make a lot of money selling papyrus to Migdol and Tyre.
The Ratings Overseer ('3' hot key) gives information on the mission requirements. Bring up the Ratings Overseer, click on Prosperity, and the game will probably confirm that the problem is that the city lost money.
By the way, I recommend playing at least the first dozen or so Pharaoh "family history" missions (to learn the basics, such as making money and raising Prosperity) before trying Cleopatra.