The Error Message

• The third line (beginning with a "!") is the error indicator (what the error is).
• Next two lines tell what (La)TeX was doing.
• Next, the error locator
  • Sometimes (La)TeX has passed the true error. . .

Your Options

• Type "X" or "x" and "return" to stop compilation.
• Hit "return" to allow the compiler to continue. . .
  • Isolated errors. . .
  • Error cascades. . .