During Sharepoint solution deployment, in case of an anomaly "A deployment or retraction is already under way for the solution and only one deployment or retraction at a time is supported" error is encountered.
To avoid this problem, refer to the following steps:
Locate deployment jobId to break the running process using following command:
C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN>stsadm-o enumdeployments
Then cancel the deploy typing the following command:
C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN>stsadm-o canceldeployment-id "GUID jobId"
Check that deploy has been canceled by typing the following command:
C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN>stsadm-o enumdeployments
Hope it helps!
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