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The error, "Illegal start of token," intermittently occurs when synchronizing in Collector for ArcGIS (iOS) through the Web Adaptor.

Last Published: October 23, 2015 ArcGIS for Server
Bug ID Number BUG-000081991
SubmittedSeptember 19, 2014
Last ModifiedJune 11, 2020
Applies toArcGIS for Server
Version found10.2.2
Operating SystemWindows
Operating System Version7 64 Bit
Version Fixed10.4

Additional Information

Resolved with the 10.4 release of ArcGIS Server and/or ArcGIS for Desktop.


Increase the uploadReadAheadSize value on Internet Information Services (IIS) to fix the issue: 1. Launch IIS Manager.2. Select the site that is hosting the web application.3. In the Features section, double-click Configuration Editor.4. Under Section, select 'system.webServer', then 'serverRuntime'.5. Modify the 'uploadReadAheadSize' section to 20 MB (Bytes).6. Click Apply. During the renegotiation step, the entity must be preloaded using Secure Socket Layer (SSL). The result is larger than the default value.

Steps to Reproduce

Bug ID: BUG-000081991


  • ArcGIS for Server

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