<td class="prop">
<g:textField name="dimensions[${i}].value"
value="${fieldValue(bean: q, field: 'value')}" />
</td>
This is due to the construct [${i}], to resolve the problem wrap the i variable in braces [${(i)}]<td class="prop">
<g:textField name="dimensions[${(i)}].value"
value="${fieldValue(bean: q, field: 'value')}" />
</td>
The error then disapears.