Error “Cannot map GET”

This is an error I’ve been seeing in the error logs. Any clues as to what’s causing it? Please note, at the end of the long list of numbers is the text “/request_format~html/ HTTP/1.0 to file” (perhaps it may be of help?)

(36)File name too long: [client 68.101.121.56:45258] AH00127: Cannot map GET /default-calendar/action~posterboard/cat_ids~5874,93,28644,29868,181,5581,1700,30558,1701,15039,5875,39,28903,1346,50,169,15041,166,1343,18280,6719,87,30034,5889,6720,174,108,6743,6764,6744,6745,6746,6762,6763,1702,30064,99,13360,5605,18281,6750,18279,6747,28466,113,1154,125,1704,147,5710,18474,287,86,18034,1345,43,18366,5888,1355,1145,17815,17886,5559,15044,18276,30068,6069,6739,6727,6783,6710,6728,6740,6729,6703,6730,6709,1705,20597,20599,20601,20598,20606,20600,30555,15040,5711,5709,15042,1147,12564,15045,1356,1357,28396,1358,160,18277,18001,15043,5576,92,1148,6738,30551,18278,5188,5560,1747,5601,20657,5610,1149/tag_ids~30787,26646,25754,28362,31288,22411,31126,26469,26470,22254,31847 … lots of numbers … /request_format~html/ HTTP/1.0 to file