When you save or preview the form design using the Preview PDF tab, a variety of errors appear in the the Report palette. Some of these errors appear in the Log tab. Generating log messages reduces performance. Try to resolve as many of these messages as possible.
For example, you may be able to resolve messages about font substitutions by ensuring that the appropriate fonts are available. Some messages are generated even when forms are working properly and you may not be able to resolve them.
As you work in the form design, other messages, such as target warning and scripting errors, generated by LiveCycle Designer ES appear in the Warnings tab of the Report palette. Although the warnings and error messages that appear in the Warnings tab do not affect performance, they need to be fixed before you deploy the form.
You can check for messages in the LiveCycle Designer ES Report palette. You can also see these messages in the LiveCycle Forms ES log files. For more information about the messages in the Report palette, see About warning messages.
You should always review both types of generated messages. Even if LiveCycle Designer ES does not generate messages, the LiveCycle Forms ES environment may be significantly different from your desktop environment.
The form uses a font that is not available to LiveCycle Forms ES and an available font was substituted. If the form appears correctly using the substitution font, you can eliminate this error by changing the form objects to use the substitution font. You can also resolve this error by installing the missing font for LiveCycle Forms ES.
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“Script failed (language is JavaScript; context is…)”
The script cannot execute because of scripting errors. If the script does not produce results in the form, this error may not be detected when the form is tested. However, generating the error affects performance.
script = function testFractionDigits(maxDigits)
{
   index = this.rawValue.lastIndexOf(“.”);
   if (index >= 0)
   return (((this.rawValue.length1)index) <= maxDigits);
   return true;
}
In this example, index is an undefined variable. To resolve this error, add var in front of the first instance of index.
An image field object is rendered as non-interactive in Acrobat 6.0.2 Professional and Acrobat 6.0.2 Standard and Adobe Reader 6.0.2 forms. To resolve this message, convert the object to a static image object.
A subform has a row layout type that should be nested inside a table parent, but it is not enclosed in a table. To resolve this error, move this subform into a table or change the subform type to Positioned Content or Flowed Content.
See also 

Resolving log messages for optimal performance