If you get an error related to conditionals, first double check that your syntax is correct by rereading the conditionals syntax article.

Next, if you're doing any conditionals like <IF {LINKTEXT}> on a field that can contain freeform text, try changing to the BOOL version of the template variable: {LINKTEXTBOOL} instead of {LINKTEXT}. The BOOL version will return true or false which eliminates the chance of unexpected characters messing up the conditional.

Make sure you have the same number of opening <IFs and closing </IF>s. Make sure that if you open an <IF within a toplist or other repeated area that you close it within that same area.