just to follow up, if I change the form action to action="[[~22]]", I am able to avoid the makeURL() error, but my search doesn't work. My search results pages are returning urls as such:
http://mysite.com/search-results.html?id=&asId=
my trace stack shows the following:
[2016-01-13 14:54:22] (ERROR @ /index.php) `[[+landing]]` is not a valid integer and may not be passed to makeUrl()
[2016-01-13 14:54:22] (ERROR @ /index.php) #0 /home/mysite/dev/core/model/modx/modparser.class.php(1330): modX->makeUrl('[[+landing]]', '', '', '-1', Array)
#1 /home/mysite/dev/core/model/modx/modparser.class.php(476): modLinkTag->process(NULL)
#2 /home/mysite/dev/core/model/modx/modparser.class.php(247): modParser->processTag(Array, true)
#3 /home/mysite/dev/core/model/modx/modchunk.class.php(118): modParser->processElementTags('[[$TopSearchFor...', '<form id="[[+as...', true, false, '[[', ']]', Array, 10)
#4 /home/mysite/dev/core/components/advsearch/model/advsearch/advsearch.class.php(387): modChunk->process(Array)
#5 /home/mysite/dev/core/components/advsearch/model/advsearch/advsearchform.class.php(142): AdvSearch->parseTpl('TopSearchForm', Array)
#6 /home/mysite/dev/core/cache/includes/elements/modsnippet/88.include.cache.php(37): AdvSearchForm->output()
#7 /home/mysite/dev/core/model/modx/modscript.class.php(70): include('/home/mysite/...')
#8 /home/mysite/dev/core/model/modx/modparser.class.php(513): modScript->process('&landing=`22` &...')
#9 /home/mysite/dev/core/model/modx/modparser.class.php(247): modParser->processTag(Array, true)
#10 /home/mysite/dev/core/model/modx/modresponse.class.php(83): modParser->processElementTags('', '<!DOCTYPE html>...', true, false, '[[', ']]', Array, 10)
#11 /home/mysite/dev/core/model/modx/modrequest.class.php(145): modResponse->outputContent(Array)
#12 /home/mysite/dev/core/model/modx/modrequest.class.php(129): modRequest->prepareResponse()
#13 /home/mysite/dev/core/model/modx/modx.class.php(1412): modRequest->handleRequest()
#14 /home/mysite/dev/index.php(69): modX->handleRequest()
#15 {main}